Moetai

Taichi is a fat teenager and a horrible embarrassment to his little sister, Mika. She saves her own image by refusing to acknowledge him in public, but that won't work forever. In order to solve the problem, she enrolls him at a boxing gym, hoping the exercise will make him lose weight. At first, Taichi is very hesitant about the whole idea. Soon, though, his trainer Kurata's tough encouragement makes him feel like he might actually be able to become good at this sort of thing. But while the boxers at the gym accept him as a fattie coming in to jump rope and hit punching bags, will he be able to get them to accept him as a boxer-in-training? And does he have what it takes to become an actual boxer?

(Source: MangaHelpers)