Hero-ga Jipchakaneun Akdangi Doeeotda

Da-in, ended up possessing the villain of a story. To make Stardust—the story's protagonist and his favorite character in a dystopian manga—happy, he resolves to become the villain Egoistic for her growth. Da-in deliberately causes terror to enhance Stardust's abilities and preemptively prevents all the tragic events from the original story, but in the process, he gains public support while also drawing Stardust's suspicion. Stardust, who initially opposed him, gradually opens her heart, and soon even begins to show signs of obsession toward him...?

(Source: KakaoPage, translated)