Masayuki Mizutani anticipates having some time to himself while his parents are away on a lengthy business trip. However, upon returning home, he finds Sayaka Shimizu, a schoolmate, waiting at the door in little more than an apron. Sayaka is a family friend whom Masayuki's parents requested to supervise him during their absence, and she has devoted herself entirely—mind, body, and soul—to fulfilling this duty. Yet, when other young girls attempt to get close to Masayuki and his newfound liberty, Sayaka pledges to do whatever is necessary to keep him exclusively for herself.