This is from a doujinshi/hentai called “See Saw Game”, by an artist called Hayabusa Kato/Katou.
This artist is known for primarly making doujinshis about female weight gain. Unfortunately, he doesn’t do any male weight gain. However, he stills includes fat males in his works. For example, here, he explained he wanted to break the cliché in porn works of a “big girl with a skinny guy”, because often “couples look quite similar”.
The story here is the following: this overweight boy is the boyfriend of one of the prettiest girls in school. He thinks she has a fetish for fat guys, but she soo reveals that she has a fetish for big breasts, and that she is jealous of his chest, which is bigger than her. She ends up asking him to make her fat, so she can have big breasts.
He accepts and makes her eat just like he does, which means a ton. Like he says, he is always “surprised” to see that other people can eat just little quantities and stop themselves from eating. To give you an idea of his diet, not counting the usual meals, he has several bento boxes to eat between periods, he snacks whenever he has free time, and if he can before going back home he goes to a fast-food.
Funnily enough, he explains to her that even with this much food, she won’t become as big as him until several years. She ends up being bigger than him in a matter of weeks (or months? Can’t remember) and she becomes even bigger than him by the end of the year. That’s when he realizes that his eating habits may be bad.
WoodsGotWeird 