In this world, dungeons suddenly appeared and people called the Awakened, who have both levels and skills, began appearing among humanity.

Yuu Kanbase gained the Immortality skill and decides to go back in time with an item he can gain from clearing the Eternal Dungeon, the hardest dungeon in the world, to save the family that he couldn't protect in the past. He continued to challenge the dungeon for 10,000 years. He finally reaches the peak where he faces off with the dungeon master, the demonic dragon Anglaus. Yuu wins the life-or-death battle and manages to go back in time, but for some reason, Anglaus also remembers what happened before Yuu went back in time...