High schooler Natsuo is hopelessly in love with his cheerful and popular teacher, Hina. However, one day at a mixer, he meets a moody girl by the name of Rui and ends up sleeping with her. Soon after, his father announces that he's getting remarried to a woman with two daughters of her own. And who shows up in tow, other than both Hina and Rui?! Natsuo's outrageous new life starts now!
Hina, Natsuo's new step-sister and crush, is having an affair?! Natsuo and Rui join hands, and together, they frantically try to track down her scandalous lover. At last, they come face to face with the man in question, Shuu Hagiwara! However, Shuu declares that he has no intention of breaking things off with Hina. Just what sort of conclusion awaits this twisted relationship?!