Knockin' on the Dungeon Door

One day, faint-hearted Hyeon-Bok Kim opens his apartment door and is startled to find a dungeon full of monsters instead of the world he knows. At first, he hides. But when all else fails, it falls to Hyeon-Bok to defeat the dungeon bosses or die trying. Luckily, he’s not alone. With the help of his skeleton friends (and a gift from a mysterious benefactor), he develops his rare talent for magic while learning about bravery and friendship. Hyeon-Bok seems ready to face whatever the dungeon throws at him… but is he?

(Source: Tapas, edited)