The Unwanted Undead Adventure Season 1

The anime "Unwanted Immortal Adventurer" tells the story of Rent Fine, an adventurer who did not seek eternal life but unexpectedly obtained it. He was a regular adventurer, engaged in the extermination of goblins and other minor evils. After ten years of endless battles in the dungeons of the Water Moon, Rent discovers a secret passage that leads him to a fateful encounter with a hungry dragon. After the dragon devours him, Rent revives as a lich - a sentient being resembling a zombie.