Fuuma Kotaro, a ninja, is a Kagemusha (body double) for Houjou Ageha, a princess. He masquerades as her when they go to school.

The minister's aide has an idea, a project in mind to help correct the declining birth rates in Japan. This plan, so to speak, has it where Japan's youth are encouraged to form relationships. The catch is that at the chosen high school for the initial test of this is being held, the project is mandatory - the students must become intimate couples with the other students or they will die.