Toshiko Sato

Toshiko "Tosh" Sato 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 remains a mystery.

Early life
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; however, her logout screen in "Exit Wounds" gives her date of birth as 19 September 1981 and REF: Torchwood: The Encyclopedia gives her birth year as 1975)

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)

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 a woman 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. After the defeat of her former lover, Mary, she decided to destroy the pendant, fearing what consequence such a device could have for humanity. (TW: Greeks Bearing Gifts)

Later, 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, 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 Cooper, 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.