There are six races in this world: human, beast, dragon, elf, dwarf, and demon. Humans are discriminated against and looked down on as the most inferior race. The "Gathering of Races" was a party with members from each race gathered to dispel such discrimination, but they also had a hidden purpose. They were ordered by the non-human countries to search for the human "Master," and take it to their own country.

Light, a human boy with the gift "Infinite Gacha," was welcomed into the Gathering of Races as he was suspected of being a Master. But in the end, their investigation showed that Light was not a Master. Just as Light was about to be killed by his teammates, he accidentally stepped on a transfer trap and was teleported to the lowest level of the dungeon.

In the deepest dungeon, he was attacked by a mythical level 1000 demon. In a desperate situation, Light used "Infinite Gacha" repeatedly. Luckily, he draws the SUR level 9999 card "Mei the Seeker Maid." Mei helped Light repel the demons and saved his life.

After finally escaping from the crisis, Light decides to take revenge on his former comrades. Mei advises him to remain in the dungeon and use Infinite Gacha to increase his number of trustworthy friends. Light agreed began building up the power necessary to oppose the non-human nations.

Three years later, Light had built the strongest nation in the depths of the dungeon. Once again, he will return to the surface to take revenge on his former comrades and search for the truth that nearly killed him.