Jinjja X-dwaetda

Byung-Jin, a straggler with no girlfriend, no friends, no popularity, and no one else, musters up the courage to confess to Seon-Ah, the girl he fell in love with at first sight, at his high school entrance ceremony, but fails. Disheartened, Byung-Jin, with the encouragement and help of his classmates, tries again, but fails miserably. Deeply frustrated, Byung-Jin is about to give up on everything, when a female student appears and makes him a crazy proposition: "You, become the main character of my comic book."

(Source: Kakaopage, translated)