The Warrior Returns

After saving one world, warrior Minsu Kim returns to Earth only to find that he's lost everything... so he decides to destroy the world he used to call home. In his rampage, he kills teenager Jeongsu Park and his family. But instead of dying normally, Jeongsu is transported to another world, where he finds that he's now a warrior himself. After killing the demon king of this alternate world and honing his skills as a warrior, Jeongsu returns to earth, hell-bent on revenge against Minsu. As the two warriors fight with the fate of their country in the balance, who will emerge victorious?

(Source: Webtoon Entertainment)