Shungo Ninomiya, a typical high school student living with his mercenary sister Ryoko, has his life turned upside down when a helicopter drops off Mayu Tsukimura, a cute girl who happens to be a succubus, and her incubus brother Mikihiro to live with them. Tasked by Ryoko to help Mayu conquer her fear of men, Shungo faces a series of awkward situations, including sharing a bed and bathing together. As if that's not enough, the student council president, Reika Houjou, joins as their maid, determined to sabotage their intimacy training. Amidst these bizarre events, Shungo's once ordinary existence spirals into chaos.