Toshiko Sato's mother

Toshiko Sato's mother, like her father, served in the RAF. (TV: Greeks Bearing Gifts) She suffered racial prejudice during World War II, possibly relating to Japan being one of Britain's enemies and stories of Japanese soldiers treating British POWs terribly. (TV: Captain Jack Harkness) She gave birth to her daughter in London in 1975 but two years later, they moved to Osaka, Japan. (TV: Greeks Bearing Gifts)

She enjoyed jazz music. This influenced her daughter into liking jazz music herself. (PROSE: ''SkyPoint)

In 2005, she was kidnapped by Milton as a way for Milton to get her daughter to work on a sonic modulator. Milton tested the sonic modulator on her. (TV: Fragments) A vision (perhaps induced by Bilis Manger) of her mother with blood running down one side of her face urged Tosh to turn against Jack with the rest of the team and open the Rift. (TV: End of Days)

Behind the scenes
Given the appearance alongside ghosts in End of Days, it is possible that Mrs Sato was killed by Milton in Fragments. However, Jack mentioned that Tosh could contact her mother every once in a while.