One Pound Gospel

(from ebookjapan):

Kosaku Hatanaka is the head of the Mukoda Boxing Gym. However, he has a weak will and is not good at losing weight. He is in love with Sister Angela. Sister Angela, a nun at St. Mary's kindergarten, is also in love with Kosaku.

Kosaku Hatanaka is a young boxer with natural talent and strange luck. However, he has no guts (!?). He can't stand to eat even before a match, and the president of the gym takes good care of him. Kosaku goes to his love, Sister Angela, to repent for his sins, and she supports him wholeheartedly.

Kosaku throws up in the ring during a match, and is banned from future fights because he is "the scourge of the boxing world. Meanwhile, the opponent he accidentally punched during a road war is a professional boxer and asks for a match to make up for his grudge. Unaware of the circumstances, Kosaku enters the ring again. Will his natural talent and strange luck work?