Living with his frequently absent mercenary sister Ryoko, Shungo Ninomiya is an average high school student until he meets Mayu Tsukimura, a succubus dropped off at his school via military-grade helicopter along with her incubus brother Mikihiro. Ryoko has arranged for them to stay with the Ninomiyas, but Mayu's androphobia poses a challenge for Shungo, who is tasked with helping her overcome her fear. To get closer to Shungo, Mayu is urged to share his bed and take baths with him, which makes him uncomfortable. Things escalate when the student council president, Reika Houjo, joins them as their new maid to prevent any sexual tension between Shungo and Mayu. The arrival of these oddities throws Shungo's once ordinary life into chaos.