"You're impure." Toki, a man who claims to be an immortal mononoke, and Yashio, a high school student who is suddenly told that he is impure. In the name of purification, a strange living arrangement between the two begins. Although Toki is nothing but teasing words and actions, Yashio can taste the loneliness he occasionally exhibits. As they spend time together, Yashio feels more and more drawn to him. However, knowing that Toki already has a loved one— 「ケガレている」不老不死のモノノケだという男・トキに突然そう告げられた高校生・八潮。八潮についたケガレを落とすという名目で、ふたりの奇妙な同居生活が始まった。揶揄うような言動ばかりのトキだが、時折見せる孤独に触れ、共に過ごすうち心惹かれていく八潮…しかし、トキに想い人がいることを知り――。