Tada no Shikabane Youda Toiwarete Ikuseisou, Kidzuitara Saikyou no Undead Ninatte Ta (Associated Names)

Zion, a solo adventurer, recklessly entered a dungeon beyond his ability. Alas, that was the last thing he did. Wandering inside a dungeon for hundreds of years, as an undead, he kept advancing into the dungeon. Slaying monster left and right until his undead body underwent ‘evolution’ many times over―― ―― By the time he…