Dogs and the Brave Are Not Showy

Sousuke Satou, 18 years old (elementary school graduate), was summoned to another world, defeated the demon king, and returned to Earth for the first time in several years. While he is unable to find a job anywhere and lives a part-time job, he encounters a battle between a "magician" and a "monster" who he thought did not exist on earth! Sousuke easily defeats monsters, but that power catches the attention of others, and he ends up getting involved in demon subjugation...?! The former strongest hero takes part in modern, supernatural battles!!

(Source: Overlap, translated)