The man after being abandoned by his wife had to take care of his two sons and Yayoi.
Neither her father nor step brothers cared about her, so she began to act as masculine as possible to be noticed by her family.
Because of her boyish behavior, Yayoi got molested at school, so to stop the bullies, she started taking judo classes. She began using her judo skills to defend herself, but stopped doing it due to a serious wound she made on a boy.
Years later she entered high school, masculine as always, but with a rather feminine body.
One day, a boy she liked invited her to a school party, where the guy got drunk and sexually abused Yayoi. Knowing her feelings towards him,
he confessed he was just fooling around with her and that she was an idiot for falling for him. Angry and full of hate, Yayoi strongly hits the guy in his crotch. At that moment, her mind changed. Why continuing being nice if people don't treat you the same way? Yayoi made a decision: to be and to do what she wanted. She drastically changed from being reserved, shy, and without confidence in herself, to a cheeky, unconcerned girl and without interest in the thought of the others. Fights started when the friends of the guy she punched approached to beat her in revenge. Due to the rebellion phase she was developing and the countless times she was getting into fights, her school decided to expel her.
It wasn't important for Yayoi's father how his daughter had changed and where she was getting herself into, but he didn't want the fault to lie with him. For that reason, her father made her live alone and enrolled her in Kuso Academy. He thought that kind of atmosphere would be suitable for her, and he was right.