Tada no Shikabane no You da to Iwarete Ikuseisou, Kizuitara Saikyou no Undead ni Natteta

Zion has always dreamed of becoming a great adventurer, so he leaves his small hometown in the boonies to head for the city. He is able to quickly move up in the ranks, until he suffers a fatal wound in a dungeon far beyond his abilities and his dreams are cut short. As he lays dying, his blood is mixed with the essence of a just-fallen dragon. For hundreds of years, his soul is steeped in this mixture... and then he reawakens as the strongest undead!

With shocking white hair and blood red eyes, Zion is the very epitome of an undead, a race feared by humans for their lack of self and vile nature. However, unlike most of his kind, he retains his memories and (admittedly shy) personality from the past. Wielding unimaginable power but none of the will to use it, Zion journeys across an unfamiliar world, searching for a way to finally end his own life. From corrupt necromancers to all-powerful dragons, why can't any of them lay a scratch on him?!

(Source: MAL Rewrite)