HAPPY FACE

Happy, who grew up as a slave in the arena, has survived with monstrous skills. When the arena owner is executed, Happy is freed and meets new family and friends, gradually learning about society. However, the world did not give Happy the chance to stop fighting. As his identity, war on crime, and the secrets of his birth continue to intertwine, Happy becomes a being who goes beyond a monster and stands at the top of the world.(Source: Naver, translated) — Description from AniList community (anilist.co).