To solve the disastrous declining birthrate problem accompanied by simultaneous reduction in male individuals' reproductive abilities, the authority has conducted "futanarification of women" based on genetic technologies. However, there arises a problem that the new sex "futanari" cannot leave male offspring. Nowadays, the sex ratio is out of the normal range as women and futanari occupies 94% of the population, and men are driven into the rest 6%. Akira and Kei's academy is located inside the "Boys Protection District" that is isolated from the society. They thought that they will grow up well in the academy and go out to get along with the society. However, misfortunes always befall without prior notices... Informed that his beloved elder sister is hospitalized due to an emergency health problem, Kei goes out of the academy and heads to the hospital. There he confirmed that his sister is OK. But when he is about to return to the academy, he is stopped by a nurse... He later takes the worst choice... Given that he devoted himself to protect his sister, where will his path ends...?