Danshi Koukouseiteki Kazoku Keikaku! summary:

Hino-kun is good-looking and a rumored delinquent. Actually, he is a kind-hearted high school student who looks after his young nephew. He can see that Mizusawa-kun is good at making sweets so for the sake of his fatherless nephew, he asks him to, “Please marry my older sister!” But instead, he receives a reverse proposal from Mizusawa saying, “I want to marry you.”…?!