Kurayami Santa

In the midst of Shouwa era Japan, greed runs rampant through the bustling cities and communities of the nation. King of Hell Enma Daiou summons an envoy into his office in the form of a small boy named Kurayami Santa. Through Enma's debriefing, Santa learns that the amount of greed and selfish behavior produced by humans will soon create an enormous wave of souls entering into Hell simultaneously, which would be catastrophic for Hell itself.

Santa is given one mission: do something about it. With neither guidelines nor rules, Santa is tasked to handle the situation as he sees fit. In the human world, a rampaging thunderstorm strikes a nearby cemetery with a bolt of lightning, and the envoy of Hell appears.

Teleported into the human world, Santa quickly realizes that humans are just as wicked as Enma had described. Without upsetting the balance between light and dark, Santa begins his quest to complete the mission from Hell and restore order to the human world.

(Source: MAL Rewrite)