Hatanaka Kosaku is an aspiring boxer with a powerful knockout punch. However, his lack of dietary discipline means he often crams greasy hamburgers right before a fight, forcing him to compete in higher weight classes. When he receives a sharp abdominal blow, he vomits, a humiliating incident that typically costs him the match. Struggling to overcome his weak willpower, Hatanaka meets Sister Angela, a novice at a local convent. While Sister Angela strives to help him strengthen his resolve, his presence makes her training as a nun more challenging.