Toshiko Sato

Toshiko Sato, also known as Tosh, was a member of Torchwood Three in the 2000s.

After being imprisoned by UNIT for assisting criminals under duress, Tosh was released by Jack Harkness under the condition that she work for Torchwood for five years. She was quiet and unassuming, generally using her computer genius to avoid exposure and to assist her colleagues. Nonetheless, she proved herself to be a field agent capable of taking on her own missions and projects. She had feelings for Owen Harper that she did not make known to him for quite some time.

She suffered a gunshot inflicted by Gray and died saving Cardiff from nuclear meltdown. However, she felt that she had failed Owen, who died unaware that she too was moments from death.

Early life
Tosh was born in London in July 1975. In 1977, her mother and father, who had both been in the RAF, moved with her to Osaka (TV: Greeks Bearing Gifts; AUDIO: torchwood_cascade_CDRIP.tor) where they lived with her grandmother. Her parents taught her English. As a child, her favourite programme was Science Ninja Team Gatchaman. (PROSE: Trace Memory) She had a brother whose death she felt responsible for, believing that she had abandoned him. (AUDIO: torchwood_cascade_CDRIP.tor) Their grandfather had worked at Bletchley Park. (TV: Greeks Bearing Gifts)

Whilst living in Osaka, Tosh was read fairy tales about Sentaro. At the age of five, she met Michael Bellini, who had time travelled into her bedroom, and was threatened by a Vondrax before Bellini left. (PROSE: Trace Memory) She was a big fan of Steve Ross's comic books, (AUDIO: Believe) was obsessed with Tetris (AUDIO: Zone 10) and was part of her school's Maths Club. (TV: Adam) In 1986, the Satos returned to the United Kingdom. (TV: Greeks Bearing Gifts)

Because Tosh always forgot her mother's birthday until the day after, the family started celebrating the birthday a day late. (AUDIO: Torchwood: SUV) When she moved into her own flat, she chose not to have a flat-warming party as there was nobody that she wanted to invite. (TV: Adam) She was "snapped up" by a government think tank at the age of twenty (TV: Greeks Bearing Gifts) and was hired at the Ministry of Defence's Lodmoor Research Facility. (TV: Fragments) At some point, she started attempting to decode Pulse. (AUDIO: Zone 10)

Joining Torchwood

 * See the behind the scenes section for the varying accounts of the date Toshiko joined.

Whilst working at Lodmoor, Milton took Tosh's mother hostage and blackmailed her into stealing the Ministry of Defence's plans for a sonic modulator and building one. The plans were flawed, however, and she corrected the design without thinking about it. After handing the sonic modulator over to Milton, UNIT arrested Tosh and withdrew her rights as a citizen, holding her in a prison indefinitely to make an example of her.

Tosh was held without right of appeal, communication with anybody outside of the prison or news of her mother's fate until she was visited by Jack Harkness (TV: Fragments) eight months later. (PROSE: The Torchwood Archives) Offered her freedom, limited contact with her mother and a clean slate in return for five years of work at Torchwood Three, Tosh accepted, (TV: Fragments) occupying the position which Jack originally hoped to fill with Nisha. (AUDIO: War Chest)

Early years
Taken to the roof of the Cardiff Bay Millennium Hall by Jack on her first day, (AUDIO: Dinner and a Show) Tosh worked alongside him and Suzie Costello (TV: Fragments) as the team's computer expert, with part of her job being to cover up the deaths of those murdered by aliens. (TV: Everything Changes) She did not have the time for a relationship given the nature of her job, (TV: Day One) but she did develop feelings for Tommy Brockless, whom the team unfroze for one day every year. (TV: To the Last Man)

Investigating the disappearances at Chelmsley Grove Psychiatric Unit, Tosh was sectioned and given medication which made her uncertain of her past and her mission until Steffan Blayney lowered her dose to help her. She convinced new arrival Shireen Afzal that she was not insane and the two of them discovered that more than seventy heavily medicated non-white patients had been taken to the Seg, home to psychovores which were whipped into a frenzy by the amount of drugs the patients had been given. After Shireen was killed, Tosh spiked Felicia Haynes and the staff of the facility with medication to set the psychovores on them, allowing the patients to escape. (AUDIO: Suckers)

Tosh, Jack and Suzie were temporarily frozen in a time bubble in the Hub for a day on the orders of Yvonne Hartman so that she could steal the team's Drahvin scanner. Upon seeing Tosh, Yvonne remarked that she was "cute". (AUDIO: One Rule)

The team were joined by Owen Harper, (TV: Fragments) for whom Tosh had to step in to replace in his second week when he was unreachable due to a hangover. She posed as a medic (TV: Exit Wounds) or xenobiologist (PROSE: Operation London) and examined the space pig at Albion Hospital, where she met the Ninth Doctor after the pig attacked her in a panic and learnt from him that the pig was not an alien. (TV: Aliens of London)

Torchwood wanted to gain access to the Antebellum and learn what was inside, so they tricked the Dow Cohort into abducting Tosh for a raid which they made sure that UNIT knew about. Vernon Roden and Nisha Bhati kidnapped her as planned and she harmed Edward Strong with a corrosive substance to give them the opportunity to enter the Antebellum disguised as medics, after which she kept Edward alive with a Serodin amplifier and manipulated Vernon into going to the "heart of Torchwood", which was full of receipts. She worked out that Edward was with UNIT Black Ops and killed him using a cancellation wave to prevent UNIT from claiming the Antebellum. (AUDIO: War Chest)

Ianto Jones persuaded Jack into letting him join Torchwood Three (TV: Fragments) and he, Tosh, Owen (TV: Day One) and Suzie wondered about who their boss really was. (TV: They Keep Killing Suzie) Tosh seemingly ruled out that Jack was a US citizen given that none had been born with his name in fifty years and disagreed with Owen that he was gay; she had "watched him in action" and knew that he would have sex with anything attractive enough. (TV: Day One)

Although Tosh considered new recruit Sebastian Vaughan to be a friend, he was unkind to her, telling her that the team found her and her obsession with technology boring and that there was no real difference between the Chinese and the Japanese. She refused to kill him after he was attacked by cortex leeches and, before he died, he told her that she was and would always be unsuited to Torchwood. She took his body to Madeline Vaughan at Rockfell Hall, blaming herself for his death, and saved Madeline from Sebastian's leech-possessed corpse. (AUDIO: The Vigil)

In her third year at Torchwood, Tosh told Tommy that she planned to learn to play the piano and speak Spanish. Although she did buy a book on Spanish, she never learnt to play the piano or speak the language because of her dedication to the work. (TV: To the Last Man)

Tosh once worked with Stephen Hines, who worked at Torchwood One, and gave him her phone number. They did not make contact with one another for two years. (AUDIO: torchwood_cascade_CDRIP.tor)

Owen called Tosh to arrange a clean-up at Queen Victoria Hospital after he discovered and put a stop to the Spores' replication and killing of patients. (AUDIO: Iceberg)

Joined by Gwen
Tosh joined the rest of the team in testing the resurrection gauntlet and was in charge of questioning John Tucker when they revived him, but he panicked when she told him that he was dead and told her that he did not see his murderer. She covered up the death of a hospital porter killed by a Weevil by changing the hospital's rota and planting a false witness and explained this to Gwen Cooper when she infiltrated the Hub, earning her disapproval. After Suzie killed herself, Tosh and Owen returned items that they had taken from the Hub and were kept in the dark about Jack's resurrection by him and Gwen. (TV: Everything Changes)

Tosh tracked the descent of a meteorite and was forgiving of Gwen when she accidentally released the Sex Gas from it, telling Owen to give her a break. She attempted to identify Carys Fletcher after she killed a man whilst possessed by the gas, located her home using CCTV, correctly deduced that she would go after her ex-boyfriend and discovered that she worked at the Conway Clinic. There, Tosh disagreed with Jack for allowing Gwen to offer herself up as the gas's new host, but he used a portable cell to stop and destroy the gas as it made the exchange. (TV: Day One)

After helping Jack, Owen and Gwen recover a quantum transducer from Bernie Harris, Tosh visited his mother in the hopes of learning where he found the device and looked up Tom Flanagan and Ed Morgan after Owen and Gwen saw the two whilst using it. Ed threw himself onto a knife held by Gwen, but Tosh assured her that he would have found a way to kill himself regardless based on his history of suicide attempts. (TV: Ghost Machine)

Jack sent Tosh and Ianto to track Rift energy in the Valleys in what the pair believed was a "cosy assignment" meant to impress Gwen as Torchwood neared its appraisals. They encountered the Zahir and a mist which Tosh deduced was a terraforming system and worked with Ianto to burn using the Torchwood SUV's petrol, leaving the Zahir without an atmosphere they could breathe. They then headed back to Cardiff for their appraisals, but Jack called and let them know that he had cancelled them as he and Gwen were hunting a Yeti. (AUDIO: Torchwood: SUV)

Tosh helped to defeat the Bruydac (PROSE: Another Life) and Scotus and his alien tapeworms. (PROSE: Slow Decay)

After sending a polite message to an Arcan leisure crawler sighted over Cardigan Bay, Tosh detected Lisa Hallett's heat signals in the storeroom whilst trying to find out what was causing an internal power drain and subsequently discovered Ianto's attempts to erase CCTV footage. She was ordered by Jack to put the Hub into lockdown to prevent Lisa's escape and to charge up batteries, but she used her own initiative to trip the lockdown timer and risked Lisa getting free. Returning to the Hub to stop her, Tosh, Jack, Owen and Gwen shot and killed Lisa after she transplanted herself into Annie Botchwell's body. (TV: Cyberwoman)

Tosh was sceptical of the existence of fairies and was perplexed when Mark Goodson died of oxygen deprivation despite there being no sign of strangulation and Gwen found petals in his throat. She detected rain over Estelle Cole's home despite it being a fine night and looked for other strange weather following Estelle's death, leading Torchwood to Jasmine Pierce's school where they realised that she was a Chosen One. At Jasmine's home, Tosh comforted Lynn Pierce after Roy was killed by a fairy and tried to hold her back when her daughter went to join the fairies. (TV: Small Worlds)

Following Ellie Johnson's disappearance in the Brecon Beacons, Tosh joined the rest of the team in investigating and tracked the SUV to Brynblaidd after it was stolen. She and Ianto were captured by Evan and Helen Sherman to be eaten whilst looking for the SUV and were soon joined by Owen and Gwen, but Jack saved them by driving into the building on a tractor and shooting at the cannibals. (TV: Countrycide) She suffered from nightmares about the ordeal afterwards (AUDIO: Broken) and was jealous of Gwen after learning that she and Owen kissed. (TV: Countrycide)

Tosh was approached by Mary and given a telepathy pendant which she used to hear what her colleagues thought of her, causing her to feel isolated and upset after discovering that Owen and Gwen were having an affair. She entered into her first same-sex relationship with Mary, whom she learnt was an Arcateenian and who claimed to be a political prisoner, and helped her get into the Hub to reclaim her transporter. Jack revealed that she was a murderer, however, and horrified Tosh by sending her into the Sun, after which she apologised for invading her colleagues' privacy and destroyed the pendant. (TV: Greeks Bearing Gifts)

Tosh used an apparently dormant alien artefact as a coffee coaster until it made her mug disappear, after which the team tested it with various other items until Ianto put it in the Restricted Items Archive. She also noticed that a mirror from Dwyford House reflected objects which were not actually there. (AUDIO: Restricted Items Archive Entries 031-049)

An algorithm that Tosh had created made her aware of a series of unusual deaths by organ failure, including Carl Brennan dying when his head exploded on a bus. Wanting to impress her colleagues, she investigated alone and connected Carl to Simon and his mindfulness group, which she soon discovered was being used by Simon to provide anger which he could channel to kill people. She realised that Janet had a superior power to Simon's and eventually got her to help defeat Simon, resulting in his death, after which she unsuccessfully tried to get her to leave Cardiff so that her power would fade. (AUDIO: Instant Karma)

Abigail Forehill was pointed towards Torchwood by Andy Davidson after she told him about how the people around her had been disappearing. Tosh, Jack, Owen and Gwen attempted to help her by getting her to the Hub, but they were all absorbed by the life-optimisation engine and restored two weeks later with Ianto's help. (AUDIO: Ex Machina)

The team became aware of a group trading in alien artefacts and Tosh was tasked with following whoever purchased a teleporter whilst the others destroyed the group's warehouse in the Brecon Beacons. She was caught, however, and infected with a Zagro worm which she managed to neutralise after getting a lift from Fawzia Mohammed, who helped her by driving her around Cardiff as she pursued Chris Thomas and stopped him from using the transporter. She destroyed the teleporter, confronted the man in charge of the operation before he was arrested and left a sum of money for Fawzia with a note thanking her for her help. (AUDIO: Drive)

Whilst working on a time lock at the Hub, Tosh decoded Pulse as a message for her and, not wanting her teammates to take her project away from her, she waited until she was able to go to Russia alone. She offered Maxim Ivanov information on Neil Redmond in return for his help in investigating Pulse at Zone 10 and learnt about the KVI's history with the Committee, later finding that Anna Volokova had been living in a loop since being kidnapped by the Committee. Tosh broke Anna free from the loop and was given Object 1 and a message for Torchwood; the Committee is calling in its debts. (AUDIO: Zone 10)

Back in Cardiff, Tosh reverse-engineered the locket to give good luck and had a "perfect day" in which Owen kissed her. After two days of this luck she came to the verdict that nobody should have that power, breaking her enhancements and sending Object 1 into the Rift. She confessed recent events to a bartender, having put retcon in her drinks to remove her memories of Object 1. (AUDIO: The Torchwood Archive)

Upon learning that a series of murders was connected to Pilgrim, Tosh chose to record Suzie's resurrection from her station rather than look her in the eye as she was questioned about the group. She was sealed in the Hub with Jack, Owen and Ianto after Gwen took Suzie to visit her father and Max Tresilian finished reciting Emily Dickinson as many times as he was programmed to, but she correctly guessed that the ISBN of Emily Dickinson: The Complete Poems would reverse the lockdown. She tracked Gwen's car to Hedley Point and destroyed the resurrection gauntlet on Jack's orders to kill Suzie and save Gwen. (TV: They Keep Killing Suzie)

Tosh remained at the Hub to act as mission control when Torchwood began investigating the deaths of a number of people connected to the Environment Agency and received a telephone call from Jack following his arrest for the murder of Robert Craig hinting that she should look into the Caru Clinic's DNA records. She sent Gwen and Owen to Ianto's coordinates to help after he was driven off of the road by the Arcanis Servitorus and found evidence that the clinic was being used by Craig, who was actually the immortal Thomas Vaughan, prolong the life of his clone, Simon. (AUDIO: Hidden)

Tosh believed that Eugene Jones's death was a simply road traffic accident and doubted that he had anything alien in his possession. She answered Eugene's mobile phone to his mother, Bronwen, and immediately handed it over to Gwen to tell her about his death. Later, Jack recovered a Dogon sixth eye from Eugene's body and Tosh told Gwen that they would have to leave Eugene's wake, but she asked for a further five minutes. (TV: Random Shoes)

Gwen informed Tosh by radio of Jack's kidnapping after he was taken by an agent of the Three Families. (WC: Web of Lies)

Tosh introduced herself to Diane Holmes, John Ellis and Emma-Louise Cowell after they travelled through the Rift from 1953 and supplied them with proof that they had time travelled. She initially had difficulty tracking down John's son, Alan Ellis, but eventually found that he was in a nursing home which John then visited. (TV: Out of Time)

Tosh tracked the route of Mark Lynch's van to a warehouse after his men kidnapped a Weevil and went with Jack to investigate, finding the body of Dan Hodges and leading to Tosh creating a cover story for Owen to look into the warehouse as a business owner. She disagreed with Jack when he released Janet to serve as bait as she believed that it was dangerous and inhumane, but Torchwood soon uncovered and put an end to a Weevil Fight Club. (TV: Combat)

Before she could head to London to celebrate her grandfather's eighty-eighth birthday, Tosh went with Jack to look into unusual noise complaints at the Ritz and was transported with him back to 1941 where they met the real Captain Harkness. She calculated a waveform equation for Owen, Ianto and Gwen to use to take them back through the Rift and wrote some of it in her own blood after she missed part of the equation when she took a photograph, but Bilis Manger vandalised her message to ensure that Torchwood would open the Rift. By doing so, Owen brought Tosh and Jack back. (TV: Captain Jack Harkness)

Tosh traced the origin of various temporal anomalies to the Rift and went with Owen to the hospital where they learnt that a woman infected with the Black Death had come through and Tosh saw a vision of her mother. She protested when Jack dismissed Owen and, after Bilis killed Rhys Williams, she worked with Owen, Ianto and Gwen to open the Rift, unwittingly unleashing Abaddon. Tosh believed that Jack had been killed by Abaddon, but he woke up after several days of apparent death and then disappeared, (TV: End of Days) joining the Tenth Doctor and Martha Jones in the TARDIS. (TV: Utopia)

Jack's absence
Per a manifesto written by Emily Holroyd, Tosh was made leader of Torchwood in Jack's absence due to her being the longest-serving member. She went with Owen and Gwen to investigate a burst of energy near the Fenmere estate and found its source to be a Rehabilitator, through which both Owen and Gwen viewed her and unwittingly caused her to transform to conform with their ideals. Once the matter was resolved, she decided to break the rules by putting Gwen in charge. (PROSE: Kaleidoscope)

Tosh invited Owen to a production of Faust at the Cardiff Bay Millennium Hall on Valentine's Day, but he failed to attend and she was instead joined by Ianto, who alerted her to the presence of aliens at the hall. Using her PDA, she identified the aliens as Grosche whom they discovered that Ilmatar planned to feed by burning his audience with the sympathetic vibrations of his voice. Ilmatar disappeared, although Tosh and Ianto believed that they would catch him in the future, and the pair drank Proseccio on the hall's roof whilst ignoring Owen's attempts to contact them. (AUDIO: Dinner and a Show)

Tosh, Gwen, Owen and Ianto were sent on a "wild goose chase" to the Himalayas by the Master, under the guise of Harold Saxon, to keep them from being a threat to his plans. (TV: The Sound of Drums)

After Jack's return
Tosh was pleased by Jack's return and was attracted to John Hart, who alerted the team to the presence of what he claimed were radiation cluster bombs, one of which Gwen sent her and Owen to recover from a warehouse in the north of Cardiff. John attacked them both and took it, after which Ianto found them and Tosh used her technical abilities to find Gwen, who had been poisoned whilst accompanying John. The three devices formed a DNA bomb which Tosh was unable to jam as she could not find the frequency that it worked on, but Owen managed to confuse the bomb and it was thrown into the Rift. (TV: Kiss Kiss, Bang Bang)

Following Rupert Howarth's arrival at the Hub, Tosh alerted her team to a police report concerning a creature leaving several bodies in a burning warehouse. The creature, a Chimera, later broke into the Hub and was killed by Howarth. (COMIC: The Legacy of Torchwood One!)

Tosh looked around Mike Lyndon and Beth Halloran's house with Jack and Owen after Beth killed one burglar and injured another, but she did not believe that either could have been responsible. She set up and controlled the mind probe to drill through Beth's consciousness, revealing that she belonged to Cell 114, and suggested that the team freeze her with alien cryogenics. After the Cell activated, she found that they were after nuclear warheads and, once they were stopped, she, Jack, Owen and Ianto shot Beth as she pretended to threaten Gwen. (TV: Sleeper)

When Tommy Brockless was woken up and Tosh learnt that he would have to be returned to 1918 to use a Rift Manipulator to stop a time shift, she was initially unwilling to send him as she knew that he would be executed for desertion in France. She managed to persuade him to go back and went back herself as a psychic projection when he proved too shell-shocked to activate the Manipulator, putting a stop to the time shifts spreading out across Cardiff. Afterwards, Owen made sure that she knew that she was responsible for saving the city. (TV: To the Last Man)

Tosh found that the Cash Cow's meat was being transported by Harwood's Haulage and called Rhys Williams for further information, learning that their contract was with Harries & Harries and coordinating the mission to put a stop to the operation. She realised that the creature could feed the world but sympathised with it and was the first to suggest that it be euthanised, which Owen eventually did. She also attempted to ask Owen out on a date, a request which he misunderstood as one for the entire team. (TV: Meat)

Tosh managed to get a day off to travel to London to meet with Stephen Hines after he asked for her help, telling her about a spate of disappearances in which all of the victims shared the same birthday and how it was now targeting him. She discovered that a computer virus was responsible and felt guilty when she failed to save Maximilian Ford, who was used by the virus as an interface and who reminded her of her brother. She made herself a target of the virus and trapped it in a cache in the Torchwood systems, after which she advised Stephen that he move on from Torchwood and delete her phone number. (AUDIO: torchwood_cascade_CDRIP.tor)

Adam Smith infiltrated Torchwood by giving false memories to the team, making Tosh believe that they had been in a relationship for a year and making her more confident. She rejected Owen and held Jack at gunpoint when he realised Adam's deception, but Ianto tackled her and Adam was locked up. Although she was upset to lose her false memories of her relationship, she took retcon with the rest of the team to get rid of Adam. (TV: Adam)

Tosh found a ritual motorcycle near a number of crates that washed up at Cardiff Bay and examined it, but it used drugs to possess her and used her to track down another motorcycle. She was able to lure the other motorcycle onto a section of the motorway which Jack had closed down, after which Owen helped her find mushin to restore her own mind. Drew Blayney, the rider of the second motorcycle, died and Tosh ordered both vehicles to delete their core programming. (COMIC: Jetsam)

Whilst taking a water sample from the bay, Tosh found oil containing a sentient element which replicated the forms of Ianto and The Dread and began targeting power supplies. She worked to find a way to stop the element from replicating, which was achieved using micro-organisms which ate through the oil's hydrocarbons, and she and Ianto worried that Jack, Owen and Gwen had died aboard the facsimile of The Dread. However, they emerged from the water after the ship collapsed. (PROSE: Black Water)

Tosh and Owen were kidnapped by Bilis Manger and possessed by the Dark before he transferred it into Idris Hopper. (PROSE: The Twilight Streets)

Tosh went with Jack and Ianto to recover a chrysalis from Pontcanna and tended to Owen after he was injured by the creature that burst from it in the Hub whilst Gwen pursued it. She guided Owen and Ianto to another chrysalis which came through the Rift and trapped the creature in a time field using the Rift Manipulator, later deducing that both creatures had come to Earth to settle their differences. They released the frozen creature and they both fought, with Jack killing the victor. (PROSE: Harm's Way)

After NHS systems lost a significant amount of data including that of several victims of toxic shock, Tosh looked into the supposed crash and agreed with Martha Jones that the Pharm could have been responsible. Martha went to the facility to close down the firewalls so that Tosh could access their computer files and Jack had Tosh shut down the facility upon learning of their use of Mayflies. As the evacuation began, Aaron Copley shot and killed Owen, who had agreed to go on a date with Tosh. (TV: Reset)

Tosh confessed her love to Owen when Jack brought him back with the second resurrection gauntlet, assuming that his resurrection was only temporary, and she did an analysis of the glove when he remained mobile. She saw that Owen was possessed by Death when she checked his movements on CCTV and refused to let him confront Death as it claimed souls, but he distracted her with a kiss and locked her out. Afterwards, she wondered if Owen had truly defeated Death. (TV: Dead Man Walking)

Tosh maintained hope of a relationship with Owen despite his condition, but he felt patronised and emasculated by her visit to his flat. She detected an energy spike at Henry Parker's house and supplied Gwen, who apologised for not asking her to be a bridesmaid at her and Rhys's wedding, with a schematic which Tosh later used to direct Owen through the house to find the source of the energy. She again told Owen that she loved him when it seemed that he would be destroyed by the Pulse and, when he survived, she told him to speak to her whenever he felt the need to. (TV: A Day in the Death)

When an artefact was found to be missing from the archive, Tosh went with Gwen to the Ashley ab Hugh Museum upon finding online that ab Hugh once had it in his art collection and learnt from Bill Williams of the deaths of ab Hugh and a private investigator who came looking for the artefact. They discovered the bodies of a cult and located the artefact at Arkanovitch Hotel, where Tosh examined it and found that it held a suspended nuclear explosion. (PROSE: The Beauty of Our Weapons)

Tosh was happy when Gwen went ahead with her wedding despite being impregnated by a Nostrovite and told her that she did not expect that she and Owen would ever get married. When the child's mother arrived to claim her child, Tosh hid with Banana Boat and joined Jack in tracking her down, with Jack eventually managing to kill her and Owen and Rhys destroying the child with the singularity scalpel. Owen later invited Tosh to dance with him. (TV: Something Borrowed)

When Ianto was made a slave to an alien plant in the hothouse, Tosh noticed that he looked tired and became concerned when he removed all the other plants and refused to let her take a cell sample. She used her PDA to confirm that the plant was dead after Jack stamped on it. (PROSE: Plant Life)

Tosh remained at the Hub when Owen, Ianto and Gwen went to the Electro and noticed her systems behaving oddly following Rift activity there. She ran a film found at the Electro frame by frame with Ianto, who noticed that the Ghostmaker and Pearl disappeared, and kept an eye on sightings of the Night Travellers. (TV: From Out of the Rain)

Tosh helped Gwen collect information on people who had been taken by the Rift, theorising that the negative Rift spikes she detected indicated abductions, and agreed to keep her project a secret from the rest of the team until she was ready to tell Jack. When Jack told Gwen to shut her project down, Tosh told her that they had tried their best. (TV: Adrift)

As part of Owen's mission against the Church of the Outsiders, Tosh seduced Frank Layton in order to search his house for information and forced Owen to listen to her having sex as revenge for making her do it, although she was angry with herself as well as at him. When Frank began to suspect her of being a spy, Owen shot him dead and they discovered that he had been guilty of nothing save helping the Church avoid taxes, infuriating Tosh. On their way back to Cardiff, they were astonished when Jack appeared on a Church broadcast demonstrating his immortality and rushed to aid Gwen from Greys who had infiltrated the Hub. (AUDIO: Believe)

Investigating Paul Talbot, Tosh confirmed that he was human by finding his birth certificate but reported that he seemed to be transforming into something. She traced his movements and came to believe that his DNA was mutating because of a tendril of Rift activity rather than being part of Cell 114 as Jack suggested he might have been. Ultimately, Paul chose to die and she watched as he did so, crying. (PROSE: Monster)

Tosh attended quiz night with Andy Davidson and his girlfriend Caite, impressing them with her knowledge of rivers. (AUDIO: Gooseberry)

Death
Tosh went with Jack, Owen and Ianto to an old building to investigate unusual energy patterns that she detected and which she assumed belonged to an alien species that they had not encountered before. The patterns actually belonged to explosive devices which injured the team, with Tosh suffering a broken arm, bruised ribs and needing to be saved by Jack, Ianto and Rhys from a pillar which almost crushed her. (TV: Fragments) Owen gave her painkillers so that she could help the team when John Hart and Gray started attacking Cardiff.

Investigating reports of ghosts, Tosh visited the central server building with Ianto and the two were later tasked with stabilising the Turnmill Nuclear Power Station and preventing meltdown. She was shot by Gray in the Hub as she directed Owen on restoring the coolant system and, with meltdown inevitable, she had Owen seal the power station. Owen was locked inside and Tosh spoke with him as he died, discussing the date that they had never gone on, reminiscing about their early days together and keeping from him the fact that she too was dying. She died in Jack's arms after he returned with Gwen, Ianto and John. (TV: Exit Wounds)

Legacy
As the team deleted Tosh's profile on the computer system, an automated video message she had recorded played. In it, Tosh thanked Jack for saving her life and proclaimed her love for Owen and the rest of the team. She reassured them that it was okay that she was gone, saying that she hoped that she had done good. (TV: Exit Wounds)

When faced with certain death at the hands of the Daleks, who were about to overrun the Hub, Gwen expressed her desire to "go out fighting, like Owen, like Tosh"; (TV: The Stolen Earth) she and Ianto were saved by a time-lock defence system that Tosh had been working on before her death. The Hub was sealed in a time bubble, preventing a Dalek from entering to finish them off. (TV: Journey's End)

After witnessing the deaths of a couple in a café who she had been unable to save, Gwen remembered the deaths of Tosh and Owen and how utterly powerless she had felt. (PROSE: Bay of the Dead)

After the 456 incident, Jack revealed that he felt responsible for Tosh's death, along with those of all the other Torchwood operatives who had died under his command. (TV: Children of Earth: Day Five)

The ghost of Ianto Jones' father mentioned Toshiko among the loved ones his son could have seen again if he set Syriath free from the Cardiff Rift. (AUDIO: The House of the Dead)

Whilst leaving Torchwood, Gwen mentioned how she loved Tosh, as well as Owen and Esther Drummond. (AUDIO: Herald of the Dawn)

Alternate timeline
In an alternate timeline in which John Hart took control of the Torchwood Institute and became King of the British Empire, Tosh was likewise a member of Torchwood Cardiff, but died before Gwen Cooper was recruited by the king, who recalled that her death was "very sad, and messy and painful to watch" before agreeing to never speak of it again with Ianto Jones. Nevertheless, Ianto visibly burst into tears as John decided that Gwen would inherit Tosh's desk. (AUDIO: The Death of Captain Jack)

Personality
Tosh considered herself to be a rationalist. (PROSE: Slow Decay) She was a computer genius and arguably the most intelligent member of the Torchwood team. Despite her intelligence, she was insecure and not very confident in her abilities. She didn't like to be studied. She could complete a Rubik's cube within a minute, even when Owen peeled off and replaced several of the stickers. (PROSE: Another Life)

Sebastian Vaughan said that Tosh was spineless and did not listen to her instincts, saying that she was not and never would be Torchwood material. Tosh took notice of this and decided to trust her gut more. (AUDIO: The Vigil)

Tosh was in love with Owen Harper but because of her insecurity, she found it hard to tell him how she felt. (TV: Greeks Bearing Gifts) Tragically, both Tosh and Owen were killed before they could get into a romantic relationship. (TV: Reset, Dead Man Walking, A Day in the Death, Exit Wounds)

Toshiko worried Jack. While she was at the heart of the Torchwood team, she didn't realise it. She felt more remote. Jack suspected that beneath her reserved exterior, there was a supernova of emotion which he didn't want to damage the team. (PROSE: Slow Decay)

Tosh showed interest for men and women, given her continual interest in Owen, and her romance with the female Arcateenian known as Mary. (TV: Greeks Bearing Gifts)

Torchwood website
The series 1 version of the Torchwood website had correspondence from Tosh in an unsent draft sent to her aunt discovered by Ianto. It was translated from Japanese into English by Ianto. It said that "for the last week", Tosh was with a woman, referring to Mary, "going from a schoolgirl crush on Owen through to a fantastically fulfilling sex life with a complete stranger". She called it "a week of firsts", including: Tosh's first one night stand, lesbian kiss, lesbian "shag", and the first time Tosh was late to work because of sex.

Toshiko's recruitment
Due to the inconsistent setting of Torchwood's first two series, the exact period Toshiko was recruited to Torchwood also has heavily contradictory dates.

In the television story Greeks Bearing Gifts, Mary murdered her first victim in 1812. About 196 years, 11 to 11 and a half months later, Toshiko has been with Torchwood for three years. 193 years and 11 months after 1812 would be 2006, or very late in 2005.

In the television story To the Last Man, Tommy Brockless was born on 7 February 1894 and frozen by Torchwood's alien cryogenics in 1918. Jack says "he's been here for 90 years," and "he's 24 or 114 years old." Toshiko has been present for Tommy's defrostings for four years. 86 years after 1918 would be 2004.

In the television story Fragments, UNIT's imprisonment of Toshiko happened five years ago, and Owen's recruitment happened four years ago. In the television Exit Wounds, the story that immediately follows Fragments, Toshiko mentions that she covered for Owen as a medic on Owen's second week in Torchwood during the examination of the space pig from the Doctor Who television story Aliens of London, placing Owen's recruitment in 2006, and at the very least Toshiko's imprisonment in the year before, 2005. Contradicting the chronology of Aliens of London that originally placed the story in 2006, in Exit Wounds, Jack tells the Torchwood from 1901 to freeze him for 107 years to allow him to get back to Gray. This means that Toshiko was imprisoned 102 years after 1901, in 2003, and she covered for Owen's job 103 years after 1901, in 2004.

The novel The Torchwood Archives sets Toshiko's imprisonment in late 2004 or early 2005, and Jack freeing and recruiting her eight months after this.

Other matters

 * During her first on-screen appearances, in Aliens of London, Tosh was a pathologist called in to autopsy an "alien pilot". When reintroduced in Torchwood, she was a computer specialist. In her final appearance (Exit Wounds), the character would explain this discrepancy by explaining she was filling in for Owen, pretending to be an MD because Owen had a hangover.
 * Prior to being named Toshiko, the BBC website listed her full name as Dr Hoshi Sato. Coincidentally, Hoshi Sato happens to be the name of a character in Star Trek: Enterprise.
 * Tosh left a resounding impression in the Torchwood universe and in the final episode of Children of Earth Jack admits that he feels responsible for her death. It is assumed her body was destroyed when the Hub was blown up by a bomb.
 * The name Toshiko means "genius child".
 * Toshiko was the only known member of Torchwood Three other than Jack Harkness to have met an incarnation of the Doctor. Gwen and Ianto had spoken to the Tenth Doctor through the Sub-Wave Network during Journey's End, but Tosh was the only one to have physically met an incarnation of him.