22-year-old college senior, Ryouichi. One day, he suddenly finds himself forced into a 10-day cohabitation with his sister-in-law, Arare. Back in school, they were senior and junior members of the track team. He had fallen for her and confessed his feelings at the time, only to be decisively rejected. Now, living under the same roof with her again, he feels he won't be able to restrain himself. Filled with lingering feelings and complicated emotions, these 10 days together are sure to be an intense trial.