The Outcast Returns from Another World as King of Delinquents is a Manga/Manhwa/Manhua in english language, Action 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

“I don’t want to be bullied anymore!!” Ayatsuji lori, a loner and introvert who is bullied daily by delinquents at school, finds himself suddenly transported to another world. Even in this new world, Iori couldn’t form a party and continued to fight alone, but surprisingly, he managed to defeat the Demon King in solo play! Expecting to be praised and celebrated in the new world for defeating the Demon King, Iori is instead returned to the real world by the very entity that transported him, known as “God.” To make matters worse, he is returned at the exact moment he was being bullied. Though he was unstoppable in the other world, Iori is helpless against the delinquents in reality In the midst of his despair, an unknown app is downloaded onto Iori’s smartphone…