God

God (Acoatmos) is the self-proclaimed God of the dungeon.

He has a phlegmatic personality, not caring about "good or evil" and only focusing on what he finds "interesting" due to his boredom.

The amount of time he has been alive exceeds 3 billion years and he has lost count of how long he has been alive.

He was originally a human, who helped people and granted wishes during the first 1000 years of being a god. He then got fed up with it, and instead started finding other ways to entertain himself.

In the manga, sometime later he met Mugetsu as she was also thrown into the dungeon. Like the people before her, she was struck with despairing situations. But as she continues to live on, she decides to end the despair causing dungeon by destroying many difficult monsters and providing aid to her fellow dungeon seekers with clues and other stuff. The reason she stayed in the dungeon for many millenniums is to find clues and ways to permanently kill the God.

When Junpei enters the dungeon, he was given a brief introduction about the dungeon and himself and others before him. He was watching Junpei's progress on how he continues to conquer the dungeon for his entertainment.

In the manga, Mugetsu discovered the one and only weakness that can kill him permanently during her dungeon clearing with Junpei. Mugetsu already knew that brute force was out of the options so she carefully investigated the God traces to find that weakness. She deduced that the only way to kill him permanently is to speak his real and true name in front of him. Mugetsu found his real name during her dungeon clearing with Junpei as they went their own way out of the dungeon. She met up with the self-proclaimed God of the dungeon and made conversation with him and spoke his real name. Panicking and despairing on how she learned of it. Mugetsu explains to him that it was not the end of her story, but the beginning. She then continues to converse with him and watches on from his despair and death that he deserves for the things he has done.