Kosaku Hatanaka is a natural at boxing, but he can't control his voracious appetite. As a result, he has been forced to change his weight, going from flyweight, all the way up to feather weight, something his trainer tells him he doesn't have the frame for. On top of this he accepts challenges from higher weight classes, giving his coach (and himself) constant trouble.

Into this picture steps Sister Angela, a novice nun who takes Kosaku on as a personal project, determined to set him on the right path and break his habit of gluttony. Unfortunately, closeness can sometimes breed feelings of affection, which Kosaku begins to develop. Even worse, Sister Angela realizes she's beginning to have the same problems as well.