The Hero Defeats the Bullies is a Manga/Manhwa/Manhua in english language, Fantasy series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

The hero who saved the world by defeating the demon king is summoned to a toilet bowl gang school?! A hero from another world summoned to the worst gang gathering place, "Suseong South High School." Although he is a hero who does not use his power on humans, he faces the reality of bullies like "demons" and starts true education...! Can the hero defeat the bullies and return to his own world?