Devildom

The Devildom is one of the three worlds that exist in the game. It is where demons reside, and where the majority of the game takes place. The Devildom is a distinctly different realm from Hell, presumably existing in a plane just above it.

Overview
There are eight layers to the Devildom, and as mentioned during the normal story mode, The Demon King — Lord Diavolo's father — lies willingly dormant at the very bottom. Due to this, Lord Diavolo rules as the de facto king of the Devildom.

In the Devildom, there is no sunlight. The world exists in a constant state of darkness at all times, though according to Diavolo there are different degrees of darkness depending on the time. Despite this, demons still adhere to a "day/night" schedule where they sleep and are expected to awaken in the "morning" as evidenced by the fact that the demon brothers often sit down together for breakfast and dinner, as well as go to sleep and attend school/work at specific times.

The sky and it's contellations are different from the human world's. In the Star-Crossed Lovers Devilgram, an autumn sky constellation is mentioned — the Pool of the Abyss — along with the myth associated with it. One star represents a beast, and another the maiden that was carried off by it. The nebula below the two stars symbolizes the pool created by her tears as she yearned to see her beloved.

In a text from Asmodeus, its alluded that there are four seasons in the Devildom despite the lack of a true day/night cycle. From this text, it can be assumed that the seasons function the same or at least similar to the four human world seasons, although currently (up to Lesson 16) there is no canon evidence of this aside from the text from Asmodeus.

In Shelter From the Rain, it rains in Devildom similar to the Human World. However, in Suspicious Weather, there's acidic rain which Lucifer warns that humans should avoid.

There are several ways to leave the Devildom, as per Lesson 11-4. One way is making use of one of several "external magic seals" that work as passages between worlds. All demons aside from Lord Diavolo, Barbatos, and Lucifer must receive "permission in advance" before they can use the seals. This is due to the previous misuse of their free availability. It is strongly implied that Mammon was the perpetrator.

Another method, considered the "classic route", involves an individual walking through all eight layers of the Devildom on foot. However, it is considered "too long" and, as Lucifer mentions, would destroy MC's psyche.

Witches or sorcerers can also summon individuals out of the Devildom, though there are alluded consequences to this method.

In lesson 47-9, Belphegor mentions "Devildom script", meaning the Devildom likely has their own language.

History
In Lesson 30-1, Satan and Simeon expand on Devildom history. The Devildom came into existence alongside the Celestial Realm and exists in tandem with it. Shortly after its creation, a primeval forest covered the entirety of the Devildom.

In A Special Ceremony, Lucifer mentions that New Year's is celebrated every 100 years in the Devildom.

Restaurants and Bakeries

 * AkuDonald's - a restaurant and parody of McDonald's mentioned in the chat Lord Diavolo's Fast Food Adventure
 * Café Lament
 * Cat's Eye
 * Déjà Vu - a fancy café
 * Demoning - a tea manufacturing company
 * Demon's Chocolate
 * Godevil Chocolatier
 * Headless Café
 * Hell's Burger
 * Hell's Kitchen - a casual restaurant with a bar and one of the eight job locations. Beelzebub often eats here
 * The Heinous Bee
 * Le Diable - a restaurant mentioned in the anime short
 * Le Pluvier - a restaurant mentioned in the anime short
 * Madam Devian's - a popular sweets shop
 * Madam Scream's - a popular bakery
 * Ristorante Six - a fancy restaurant and one of the eight job locations
 * Uncle Demon - a dessert shop where Beelzebub and Belphegor go to buy doughnuts

Retail

 * Akuzon Delivery Center - a shipping center and one of the eight job locations
 * "Akuzon" is a play on the enterprise Amazon and "akuma" (悪魔), which is Japanese for "devil"
 * Devilmart - a grocery store
 * Dogma Street - the biggest electronic district in the Devildom
 * Goetia - a hair salon that Asmodeus goes to
 * Hell Supermarket - a grocery store
 * Hocus Pocus - a shop that specializes in magical items and one of the eight job locations
 * Majolish - a clothing store that offers designer clothes and one of the eight job locations
 * "Majolish" comes from "majo" (魔女), the Japanese word for "witch"

Other Locations

 * The Demon Lord's Castle - Diavolo's residence
 * The Devil Planetarium
 * Diavolo's Private Beach - a private beach owned exclusively by Diavolo where it has an artificial sun
 * The Fall - a popular nightclub that Asmodeus frequents and one of the eight job locations
 * Hell Dome - likely a structure that holds events such as a sweets fair
 * House of Lamentation - the seven demon brothers' dorm; MC moves in with them in Season 1 of the story
 * Lantern Night Inn - an inn visited by the brothers and MC in the event Let the Games Begin!
 * Makai Bank
 * "Makai" (魔界) is the Japanese version for Devildom
 * The Mausoleum - one of the eight job locations
 * Purgatory Hall - the dorm for exchange students; Simeon, Luke and Solomon live here during their stay in the Devildom
 * The Reaper's Cave
 * The Royal Academy of Diavolo (RAD) - the Devildom's school
 * The Royal Library - one of the eight job locations
 * Siren Beach - a beach in the Devildom where Leviathan released Lotan

Currency
The currency used in the Devildom is called Grimm, which can be gold coins with a skull, or brown banknotes. The player also uses this currency for various expenses in the game such as upgrading cards or unlocking spaces in the devil tree. Players can obtain Grimm by clearing battle stages or sending characters to work at D JOBS. Tasks and Pop Quiz events also often include Grimm as rewards.

Food and Drink
Eating in the Devildom is a sometimes dangerous experience, as some foods are too strong, too dangerous, or otherwise inedible for MC. The rest of the Student Council looks out for MC in this regard, but there is also mention of foods from the human world. It seems that there is some mixing of foods or foods inspired by the Human World.