High school student Maruo Anai and his classmates are suddenly summoned to another world and told that they have been chosen as Heroes. While everyone around him receives rare and powerful jobs, Maruo is saddled with the seemingly worthless class of “Digger.” Declared a failure who can’t possibly contribute as a Hero, Maruo decides there’s only one thing he can do: dig. But while tunneling deep underground, he accidentally discovers a newly formed Dungeon Core. The moment he touches it, Maruo is unexpectedly registered as its new Dungeon Master. Now possessing the abilities of both a Digger and a Dungeon Master, Maruo could create a vicious death trap and take revenge on everyone who mocked him... but he really doesn’t feel like it. Instead, he fills his underground home with adorable fluffy monsters, grows delicious crops, expands his living space, and builds himself an increasingly comfortable subterranean paradise. There’s just one problem: without realizing it, Maruo keeps making his dungeon stronger. Much stronger. Before long, the supposedly useless Hero has created a dungeon filled with monsters stronger than the Heroes themselves, and the outside world has begun classifying his cozy underground home as a catastrophic threat. A dungeon-building isekai comedy about a rejected Hero who only wants a comfortable life underground, while accidentally creating one of the most dangerous places in the world.