Masayuki Mizutani is looking forward to some time to himself when his parents leave on an extended business trip. Instead, he arrives home to see one of his schoolmates, Sayaka Shimizu, greeting him at the door in barely more than an apron! Sayaka is a family friend who was asked by Masayuki's parents to look after him while they were away, and to accomplish this mission, she has fully dedicated herself—mind, body, and soul. But when other young girls try to approach Masayuki and his newfound freedom, Sayaka vows to do whatever it takes to keep him all to herself.