I am a Problematic Dungeon Master IAAPDM

In the year 2025, for unknown reasons, dungeons started appearing all around the world. Monsters started invading nearby cities and massacring the citizens. The world population was dropping by the millions each day. To fight against the monsters, the whole world decided unanimously to create genetically modified human beings called "Warriors" by injecting a serum they called "Elixir". Thus, started the counterattack of the human race.

On a certain day 12 years after the start of dungeon appearance, while raiding the last and hardest dungeon in the world, an event occurred. After getting betrayed by his teammates, Warrior Ein was pushed down a bottomless pit just before facing the last boss as a sacrifice. Regret filling his heart, he cursed at his former teammates, swearing to take revenge against them before losing consciousness.

However, when he opened his eyes, he found himself as a dungeon master in a new world. Since he will die if the dungeon gets conquered, he decided to protect his dungeon from invaders while searching for a way to return to Earth. Will he be able to return to Earth and enact his revenge?