Natsuki's first love was his private tutor, Ryogo. Unfortunately, he ended up marrying Natsuki's sister, Yukiho. Years pass by, and all Natsuki had to console himself were dirty fantasies of Ryogo. That is, until Yukiko disappears, leaving Ryogo to take care of their twins. Ryogo asks Natsuki to help with raising them, and so beings their life...