Dr. Sterben

Sterben died in a car accident and then finds himself in the middle of nowhere, surrounded by pure darkness. A nameless little angel suddenly shows up to deliver him the good news.

Sterben was informed by the angel that he is a lost soul who was given a chance to go back in the world of the living to finish a certain mission, that he couldn't remember. Failure to do the mission means he can't go to heaven.

Credits to @Sir.rikit.1230 for making the bookcover