The idea of different worlds dwelling close together is something that a lot of scientists speculate. However, there hasn't been any proof but plenty of theories and other guesses that many people have come up with. One such idea is the existence of Heaven and Hell which many religions have described using words and images. Many people from different places and regions had their own views of Hell including the various monsters that live there. As such, no one really knows what Hell actually looks like.
With many ideas of hell, the imagination of what creatures live there leaves a lot for a person to imagine. However, a lot of things that are common is that Hell is a place for the damned and where evil creatures live such as hellhounds, devils, imps, incubus, and many others. As such, there have been a lot of shows, movies, and other things about these creatures for humans to entertain themselves with.
As for those actually living in Hell, life is rather similar to life above with no actual laws ruling over them. There are several powerful OverLords such as Alastor, and Valentino along with a few others that are well known. However, the one that rules all of Hell is known as Lucifer Morningstar, the King of Hell. Of course, his appearance is nothing like how the humans above picture him....that is until something happened.
As life continues on for both worlds, an unknown force suddenly forces the worlds to merge causing a tear in dimensions causing both Earth and Hell to slowly merge. Life will drastically change for both world and especially to one person after saving the daughter of hell leading to a rather interesting adventure.
Imagine being as nice as possible throughout your whole life and then, after one bad accident, find yourself in the place meant for the most evil and terrible people ever. Y/N certainly can, because it's exactly how he ended up in Hell. Yet despite him, at first, wanting nothing to do with this realm of corruption and wickedness, he soon discovers something that makes him stay. Love. And better yet, love from many females beyond just the one that he likes. To what ends will this go? And will things work out for the new demon who just wants everything to go right?
*This is written before Hazbin Hotel's first season, so events that will play out in the story will not be entirely canon. But, hey, that's fanfiction for you.*
Disclaimer: I do not own Hazbin Hotel or its characters.