The Faraway Paladin (Manga) Volume 1 by Kanata Yanagino

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.