In the spring of Kyoko s first year in high school, Eiko, a girl like a sister to her, returns with her younger brother, Jiro. The return is not that big of a deal, but Jiro has it in his head that he wants to operate on Kyoko! And, what is even more, the two of them are actually from an organization bent on destroying world peace! As if high school did not have enough problems already, now she has to deal with these two living with her.