Kyouko is Tooru's mother.

When she was young, Kyouko caused trouble and cut classes, and was disowned by her parents following a gang fight. She hated her family, as her father felt she wasn't needed in the world and her mother only cared about the appearance of the family. She was also the leader of an all-female suicide gang. In this she was called "The Red Butterfly," the name originating from the legend of how the tail lights on her motorcycle danced like a bright red butterfly when she rode at night. However, Kyouko later moved on and got a job.

At some point, Kyouko fell in love with a student teacher named Katsuya Honda, which contributed to her leaving her gang. After she was beaten by her gang and disowned by her parents, he stood up for her and proposed to her. They shortly married and had a daughter, Tooru. Katsuya became a positive influence in her life, and they worked through difficulties in a joint effort. When he died from illness, however, Kyouko descended into a deep, almost depression-like sadness, neglected Tooru, and almost committed suicide by throwing herself into the sea, thinking she could go meet Katsuya (Kyouko had never seen the ocean before, so Katsuya took her one day). Just as she was about to jump however, Kyouko came to her senses as she saw a girl and her mother by the seaside; she came back home and found little Tooru waiting for her return at the door, similar to how Katsuya greeted her. Kyouko then vowed to never again disregard Tooru for whatever reason; she raised Tooru by herself, not to mention the care she offered Arisa Uotani and Saki Hanajima, Tooru's best friends.

When Tooru disappeared one day as a young child Kyouko was in hysterics, even going so far as to threaten the police if they did not find her. After she was eventually found by Yuki Souma, who had heard Kyouko's description of Tooru and lead the confused girl home, Kyouko was overjoyed.