Toshiko Sato's brother

Toshiko Sato had a brother.

He died sometime before Tosh joined Torchwood. The computer virus attempted to upset Tosh by accusing her of abandoning her brother to his death. It was because of her guilt that she was so desperate to save Max. (AUDIO: torchwood_cascade_CDRIP.tor)

Behind the scenes
Toshiko mentioned a brother in a deleted scene from the episode Captain Jack Harkness. She said that he was eighteen at the time that, during the events of the episode, she was transported back to 1941, and wondered if she would ever see him again.