Due to her parents' temporary absence, Kotoha is placed in the care of her relatives. However, this household is home to three older brothers—Ichiro, Jiro, and Saburo—who have yet to marry. Having had no prior relationships with women, they are deeply moved by Kotoha's innocent and pure appearance. Losing their composure, one after another falls for her. As a result, she becomes entangled with the three brothers in various ways.