Sea-Side Bound (BBW hentai comic in japanese)

This one is in Japanese, but you don't really need to understand what they say to catch the drift of the thing. A girl is trying on her bikini and notices she's gained weight. Se wants to go on a diet, but her boyfriend wants her to gain more weight, and tjhe guy comes up with a plan: the girl will eat shitloads now, becoming fat for a time, but then will go on a diet to be thin for the bikini season. The girl agrees and gorges on food, after which the pair have glorious sex. And of course, in the end the girl never loses the weight she put on.