Masamune-kun no Revenge

As a child, Masamune Makabe was rejected and mocked for his weight by the wealthy Aki Adagaki, leaving him with a humiliating nickname he never forgot. Years of relentless self-improvement turn him into a handsome, accomplished high school student with one carefully planned goal: make Aki fall for him, then reject her in return. Transferring to her school gives him the chance he has been waiting for, but getting close to the feared "Brutal Princess" proves much harder than expected. When a mysterious letter addresses him by his childhood nickname, Masamune realizes someone knows his past and could ruin his revenge before it begins.