Dungeon Juinnim

Juyoon Oh is a typical guy trying to find a full-time job. But one day, he dives into the Han River and puts himself at risk of drowning to save a child that fell in. As he is about to meet an untimely death, a goddess appears before him and gives him a chance at another life... not as a hero or a wizard, but as a weak, skill-less "brick larva." It's the beginning of an atrocious adventure, and the road to become a hero is long!
(Source: Tappytoon)