One day, the main character, Ryota, made a bet with the fellow band member, Hideto.

The bet was about who would lose the virginity faster. Yes, it was a very silly contest.

Six months later, the step sister Ririka returned to Japan from America.

Ryota could not conceal the excitement and the confusion about how much she had grown up.

Well, now it looks like Ryota is going to have some unbelievable school summer vacation in his last year in high school.

[From DLsite English]