Masamune-kun's Revenge

Adagaki Aki was the prettiest girl in their middle school, and Makabe Masamune was the chubby kid she gave a cruel nickname to in front of the class. Years of disciplined dieting and grooming later, Masamune transfers into Aki's high school as a near-unrecognizable model student with a single plan: make her fall in love with him, then dump her with the same cruelty. Aki, of course, has reasons of her own for being the way she was. The series follows the campaign of the revenge plot and the steady erosion of every assumption Masamune brought to it.