Dungeon-eul Geurineun Hwaga

In a world forever changed by the Great Cataclysm that reshaped the entire globe... Seo Jio, an ordinary art teacher, dies in a sudden fire, only to awaken trapped inside a portrait as a painting himself. Within the world of the portrait, Jio gains omnipotent abilities. He can create life and even open gateways to other dimensions. As he travels across countless dimensions, Jio encounters people bound by fate and uses his newfound abilities to help them overcome the trials before them. But with every dimension he crosses and every incident he resolves, he draws closer to uncovering the truth shrouding his own death…

(Source: Ridibooks, translated)