The Faraway Paladin (Manga)

A man dies alone after living a stagnant and fruitless life—but that''s not where his story ends, as a boy named William is born into a land of fantasy and magic.
Raised in a city of the dead by his new family—a mummy, a skeleton, and a ghost—he can remember glimpses of his past life, enough to know his time on Earth was wasted, and he vows not to let that happen again.