As a young child Tooru was heavily abused and humiliated by her father while her mother was powerless to do anything to stop it. At the age of 12, Tooru massacred her family with an axe and was taken into the care of the authorities, ruling the incident as a ghoul attack.

Tooru assumed the identity of a male while she began her studies at the CCG Academy Junior School in order for her to fit in easier. Her crimes were found out by her mentor, encouraging her dark acts and began to train her with knives. She quickly rose to prominence and was placed in the experimental Quinx squad under Haise Sasaki, whom she views lovingly and affectionately.