The 11-year-old Marui triplets couldn't be more different. Mitsuba, the oldest, is cruel and mature for her age. Futaba, the middle one, is perverse, athletic, and has the strength of a full-grown man. Hitoha, the youngest, is normally calm and polite, but when it comes down to it, she may be the strongest, most twisted, and most sadistic of the three. They are all in the same class, which is taught by the recently graduated teacher Yabe Satoshi. He is frequently pushed around and mistreated by the girls, but the triplets also try to lure him and the new school nurse, the clumsy Kuriyama Aiko, together. Yabe, on the other hand, had no intention of doing so.