Yamamoto-kun no Seishun Revenge!

Ryuga Yamamoto is a high school boy who weighs over 130 kilograms due to a strange disease called "DeBS." Because of his obese appearance, he is bullied at school, at his part-time job, and even by his mean-spirited relatives. Despite this, Ryuga is blessed with a few friends who understand him, and he tries his best to remain cheerful and tough through the adversity! After helping a classmate, Ryuga is offered a possible cure for his disease! After going to America by himself for a year, can Ryuga successfully lose weight after undergoing the painful experimental treatment with the beautiful genius Dr. Kashiwagi? The youthful revenge love comedy of Yamamoto-kun, who has a big body and a kind heart, is about to begin!

(Source: Dash X Bunko, translated)