She is a childhood friend of Konoha, who he loved very much until she attempted suicide by falling off the school building.
According to "Parumiere (パルミエーレ)" book, she actually liked and hated Konoha because the imagination was the only thing she had because of her parents' divorce. She said that by telling Konoha her imaginations to story means he stole everything about her. She also used the fact that Konoha always listened her every order to force him to be alone (away from Kazushi and Kotobuki. This is the reason to be back and to meet Konoha, to get revenge).
She attempted suicide and almost died when Konoha received the award and everyone else thought Miu Inoue was her while she just sent empty script out. She was back to the original hospital for few years without telling Konoha and met Kazushi because his mother is in the same hospital.
In an episode from Short book 1, she felt that she's superior to Konoha but felt inferior to Kazushi. He introduced her to volunteer in a Children's center.
According to 6 Year After Episode (6 years after Touko's graduation), she's volunteering in Children's center.
