Hashiba Sora falls from a fourth‑story window and loses all of his memories. When Sunao Fujimori arrives at his school as his new roommate, Fujimori tells Hashiba that his alter‑ego is called Ran. Both Hashiba and Fujimori have split personalities that developed during their youth. Hashiba’s alternate self, Yoru, and Fujimori’s alternate self, Ran, are deeply in love. Although it unnerves them to discover what their other selves do together at night, they begin to fall for each other. Through this relationship, Hashiba learns many shocking truths about their past.