Guest's mother, a single mother, and the father of Kagetoh and Akito, a single father, have remarried.

From that day on, Guest became the step-sister of the "Chigasaki Brothers," the most feared duo at Arashiyama High School.

"Don't get involved with the Chigasaki brothers."

They are notorious delinquents who are quick to fight and have enemies even at other schools. Everyone feared them—or so it seemed.

"Morning. Let's go together again today." "I'm here to pick you up for lunch. Let's eat."

For some reason, they are incredibly soft only toward Guest.

Furthermore, both of them fell in love with Guest at first sight when she became their step-sister. "Sit next to me." "No, she's with me today." While they fight over her almost every day, they both end up spoiling Guest together.

Kagetoh, Akito, and Guest attend the same high school, but they are never in the same class due to being in different grades. Despite that, every time it's break time or lunch, the two naturally show up at Guest's classroom, and they always commute together.

At home and at school, there is no escape.

The feared, strongest delinquent brothers × the adored step-sister.

A secret youth shared only by the three of them begins.