Toshiko Sato

Toshiko "Tosh" Sato (1975-2009) applied her scientific skills to the Torchwood Three team, after having worked for the Ministry of Defence. Beautiful, brilliant and insecure, much of Tosh's private life remained mysterious even after her death.

Early life
According to Mary, Toshiko was born in London in 1975. Her parents moved to Osaka, Japan, in 1977, then back to the UK in 1986. Her Japanese-born grandfather (born 20 January 1920) was a decoder at Bletchley Park and her parents were in the RAF. (TW: Greeks Bearing Gifts) Her logout screen gave a date of birth as 19 September 1981. (TW: Exit Wounds)

Later life
Around 2003 (TW: Fragments), though possibly in 2005 (TW: Greeks Bearing Gifts), Tosh worked at the Lodmoor Research Facility, run by the British Ministry of Defence. Blackmailed, with her mother's life at stake, Tosh stole plans to make a sonic modulator and successfully built one, even though the plans were faulty. She was arrested by UNIT and held indefinitely without trial, and then saved by Jack Harkness. He complimented her on making a functional model with only the schematics available and offered her a job with Torchwood as an alternative to spending the rest of her life in a UNIT holding cell. (TW: Fragments)

Life With Torchwood
Every year for a day, Torchwood Three had woken up Tommy Brockless, a World War I solider frozen in 1918. During the four years Toshiko worked for Torchwood, she fell in love with him. (TW: To the Last Man)

Toshiko met the Ninth Doctor in spring 2006 while examining an "alien pilot" in the mortuary at Albion Hospital, (DW: Aliens of London) where she was covering for teammate Owen Harper, who was supposed to carry out the autopsy but was suffering from a serious hangover. (TW: Exit Wounds) She was slightly hurt when the creature turned out to be alive. She pretended to be a medic named "Dr Sato", displaying enough medical knowledge to determine the alterations to the creature still hinted at alien involvement even if the creature itself was not an alien. (DW: Aliens of London)

In 2007, Tosh had covered up a Cardiff hospital porter's murder by a Weevil she helped capture by planting a false alibi and changing the hospital's rota. (TW: Everything Changes)

Tosh tracked the location of the meteorite containing a sex gas creature. When it escaped, she discovered the gas released ultra-powerful pheromones. Tosh cornered the creature, which had possessed Carys Fletcher, at the Conway Clinic. There, Jack tricked it into escaping Carys into the portable cell, where it succumbed to the Earth's poisonous atmosphere. (TW: Day One)

Tosh helped teammates Gwen, Jack and Owen track down the quantum transducer Bernie Harris was holding. (TW: Ghost Machine)

Ianto Jones had helped awaken the partially cyber-converted Lisa Hallett from beneath the Torchwood Hub. The team escaped, but Ianto ran back to her. After Lisa had put her mind in the body of Annie, Ianto saw Tosh and the others shoot her. (TW: Cyberwoman)

The Torchwood team travelled to the Welsh countryside to investigate a series of gruesome murders. The Torchwood S.U.V was stolen by a group of cannibals that harvested travellers once every ten years. The team followed the cannibals to their village. Right as his team were captured, Jack stepped in and incapacitated the cannibals. The cannibals were arrested by the police. (TW: Countrycide) Tosh always found Owen attractive. Despite this, Tosh had a lesbian affair, her first homosexual experience, (WEB: torchwood.org.uk) with "Mary", a female alien who tried to use their relationship to gain access to her technology, which Torchwood had previously confiscated. In order to gain Tosh's confidence, the alien allowed her the use of a pendant which granted her the temporary power of telepathy. Tosh used the device to save the lives of Carol and her child, about to be murdered in a domestic incident, but she became suspicious of the device when its use gave her insight as to how her teammates regarded her. Jack tricked Mary into being teleported into the Sun with her technology. Afterwards, Tosh decided to destroy the pendant, fearing what consequence such a device could have for humanity. (TW: Greeks Bearing Gifts)

Gwen revived Suzie Costello with the resurrection gauntlet for questioning. Tosh was unable to look her former teammate in the eye. Instead of keeping her alive for a minute for a brief interrogation, Suzie kept the link between her and Gwen. After Jack's bullets were useless against Suzie, Tosh was ordered to destroy the gauntlet, which killed Suzie and saved Gwen. (TW: They Keep Killing Suzie)

In 2008, while investigating reports of loud music from the 1940s, the Rift brought Jack and Tosh into 1941. She hid messages that preserved her half of the Rift equations that could bring her home. Owen used these to open up the Rift, bringing Jack and Tosh to the 21st century. (TW: Captain Jack Harkness)

Owen's actions had caused cracks in space and time to spread from the Rift. While cleaning this mess up, Tosh saw an apparition of her mother, telling her to reopen the Rift and undo the damage. The team turned against Jack. Owen shot Jack and reopened the Rift to send everything that had come through back. The opening of the Rift forced out Abaddon, which Jack defeated. (TW: End of Days)

Shortly after Jack's revival from this encounter, Jack disappeared from the Hub to chase after the Doctor's TARDIS parked on Roald Dahl Plass. (TW: End of Days, DW: Utopia)

Tosh was part of a "wild goose chase" in the Himalayas when Jack went missing. (DW: The Sound of Drums)

While chasing a Blowfish alien through Cardiff, Jack saved a family's life and quickly took over Torchwood again. Torchwood met an old lover of Jack's, Captain John Hart, who had came through the Rift searching for some canisters that had also come through. He told Torchwood that they contained radioactive bombs. Tosh tracked down where each of the canisters were. While searching for one of the canisters with Owen, John wounded them and stole the canister. Ianto recovered Tosh and Owen and Tosh found where Gwen had been poisoned so she could be treated. They caught up with John, but the contents of the canisters were actually components of a bomb that latched onto the DNA of the owner of the canisters' murderer. Jack and Owen confused the bomb by injecting John with the DNA of the Torchwood team and safely disposed of it. John forcibly left 21st century Cardiff. (TW: Kiss Kiss Bang Bang) During one of Tommy Brockless' yearly awakenings, the past and present time shifts began to occur, which the uniformed thought of as "ghosts". To prevent a temporal catastrophe, Tosh and the team saw to it that Tommy returned to 1918, after the couple had a short sexual relationship. (TW: To the Last Man)

She fell in love with Adam Smith when he gave her memories that they were in love and when she was told this she still couldn't bring herself to take the retcon pill until she realised it was the right thing to do. (TW: Adam) Toshiko was personally responsible for shutting down the Pharm. By that time she had actually taken the initiative to ask Owen, with whom she had feelings, out on a date. She was extremely saddened when Owen was fatally shot in the chest by Aaron Copley. (TW: Reset) After Owen's return to life via the resurrection gauntlet early in 2009, she still maintained hope for a relationship, to Owen's disgust given that his currently-deceased status prevented anything sexual from taking place. (TW: A Day in the Death) Later, however, he seemed less negative about the idea. (TW: Something Borrowed)

Toshiko and the rest of the team minus Gwen were investigating an old factory that had detected Rift activity. She was caught up in an explosion of rubble and survived by the help of Gwen but had a broken arm. (TW: Fragments)

Death
Tosh was shot by Gray while communicating via radio with Owen, talking him through his task of preventing a nuclear meltdown at a power station in Cardiff. She talked to Owen about how he would die from the meltdown and they discussed the date they had never gone on. Her wound was fatal and she died in Jack's arms after he arrived back at HQ with Gwen and Ianto. She told them how she had failed to save Owen.

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. (TW: Exit Wounds)

Though dead, Tosh's presence was still felt by the others. When faced with certain death at the hands of the Daleks, who were about to overrun the Hub, Gwen and Ianto were saved by a Time-lock defence system 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. (DW: Journey's End)

It was presumed that, per Torchwood policy, Sato's remains would have been interred within the Torchwood Hub and her belongings stored in a secure storage facility (per TW: Day One, They Keep Killing Suzie). As such, it was not known whether they survived the destruction of the Hub in 2009. (TW: Children of Earth: Day One)

Behind the scenes

 * 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.
 * 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.
 * Tosh wears a lot of purple.