After Hashiba Sora's fall from a 4th story window, he suffers from total memory loss. Fujimori Sunao becomes his new roommate at school and introduces himself as Ran. Both Fujimori and Hashiba have developed split personalities in their childhood, named Yoru and Ran respectively, who are passionately in love. Despite being disturbed by their alternate personalities' nocturnal activities, Fujimori and Hashiba begin developing feelings for each other. Their relationship uncovers startling information from their past.