Yotaro Hanafusa is a descendant of the "Knights of the World." With the Knight's Code of Chivalry hammered into him since childhood, Yotaro cannot stop himself from saving damsels in distress. He wears a mask, and is known on the street as "Knight Lancer" but he has always kept his identity a secret. While on an outing, Yotaro saves a 6-year-old girl, Makio Kidoin, the only child of a powerful business tycoon. When Yotaro discovers that Makio leads a lonely life in a huge estate, he resolves to protect her. He and his friends disguise themselves as lodgers and move into her mansion.