This list contains characters who have only been introduced in the story briefly or have been mentioned a few times at some point through the game.
The Demon King
The Demon King (悪魔の王) is the current ruler of Devildom, although he resides at the bottom of Devildom as he has no interest in the affairs of the three worlds. His son, Diavolo rules the Devildom, but he hasn't been crowned as the next king yet.
He was also responsible for the brothers' ranking and "age" when they fell from the Celestial Realm, with Lucifer being the oldest and most powerful and Belphegor being the youngest and the weakest. Despite being youngest based on birth order, Satan was deemed the fourth oldest because of his power instead of his actual age.
According to Luke, he has not seen the Demon King since a ceremony 1,000 years ago. This could've been his last public appearance.
He did have a wife, who died while giving birth to Diavolo.
Grisella
Grisella (ドリセラ) is a witch who resides in the human world. She was introduced in Lesson 10 when MC, Lucifer, Satan, and Mammon decide to journey to London to seek her help to return Lucifer and Satan back to their original bodies when the two swapped due to Grisella's magical book being touched by them at the same time. She was later killed in a train by her intended apprentice, Noah.
Noah
Noah (ノア) yearns to become Grisella's apprentice. However, he kills her by stabbing her with a knife in Lesson 11 due to Grisella continuously refusing Noah requests to be her apprentice. Grisella's spirit said that Noah once told her that he performs throwing knives in his circus act. She later reveals that she didn't take apprentices because she was aware of her impending death, but did not anticipate that Noah would kill her because of her rejection.
Mephistopheles
In the first-ever RAD Newspaper Club chat, Mephistopheles (メフィストフェレス) was in 10th place in the unofficial results of a popularity contest, but he and Mammon were disqualified due to falsified ballots. This was later commented on by Asmodeus, Satan, and Leviathan, with the latter being upset he only made the list after the disqualifications. Together with Satan, Asmodeus, and Mammon, he designed the chat-stickers Prince Lucifer and Princess Diavolo.
He used to be the president of the Newspaper Club, but was forced to step down due in part to falsified ballots, but also to the errant posts made by the Newspaper Club soon after.
Astaroth
In the first-ever RAD Newspaper Club chat, Astaroth (アスタロト) was not on the unofficial results of the popularity contest, but he earned 9th place after Mephistopheles and Mammon were disqualified due to falsified ballots.
Dantalion
Satan invited MC to the Museum, which is holding an event featuring the art of a mysterious painter that never shows their face in public. The art exposes the viewer's core, while their core also burns red and white with passion and lust. Satan tells the MC that rumors say that Dantalion (ダンタリオン) is that artist, but is unconfirmed.
Diaval
Diaval (ディアバル) is a demon who had gone to the human world as an exchange student, supposedly with Belphegor.
Michael
Michael (ミカエル) is an archangel often brought up by Luke, saying he reports to Michael directly. This implies he's in a position of authority in the Celestial Realm.
Michael loves sweets of all kinds, according to Luke in Lesson 5-12.
In Lesson 23-3, the brothers reveal that Michael always admired and loved Lucifer.
In Lesson 23-5, Barbatos refers to Michael as "Michael the Archangel. He also mentions that he's the present leader of the Celestial Realm's legion of angels and the guardian angel of confectioners.
In Lesson 27-19, it is revealed by Asmo that Micheal used to teach Mammon, but didn't know how to deal with him. This led to Lucifer taking over.
In Lesson 49, Luke has said that Michael often stares at where the demon brother's pictures used to hang when they were angels, claiming that, although he never says anything, Michael misses the demon brothers dearly.
Lucifugus
Lucifugus (ルキフグス), Asmodeus, and several others throw a party at Lucifugus' house. Asmodeus invited MC to the party, saying they will pick them up after class. He also hinted at MC getting another partner, a.k.a. making a pact with another demon.
Mahazael
Mahazael (マハザエル) is a real estate agent that tells Mammon that he has to sign a two-year contract and pay monthly rent to live on his own. Mammon believes it is a scam and tells him to "shove his two-year contract where the sun don't shine." Mahazael then tells Mammon that he will inform Diavolo and Lucifer if Mammon didn't pay.
Maddi
Maddi (マディ) is a famous witch, commonly known as the Great Witch Maddi, and possesses great power despite being a human. In the devilgram The Escorts, Diavolo asks Lucifer and Satan to escort Maddi while she's in Devildom, for they are her "type". She once aggressively pursued Diavolo and refused to return to the human world unless he married her, which he had a hard time convincing her to give up.
Mammon had gone home with her one time and the experience left him traumatized, for he had nightmares and even temporarily stopped spending money. According to Lucifer, her beauty rivals the succubus who won the beauty portion in the Queen Contest.
Little D's
Little D's are demon familiars that reside within the Demon Lord's Castle and serve under Barbatos. Little D. No. 2 has stated that each familiar has its own personality and idiosyncrasies. Not much is known about them except that No. 1 and No. 4 do not get along.
Rubezahl
Rubezahl is a DevilTube influencer invited to Asmodeus's fashion show in Lesson 32-8.
Rusalka
Mammon states that "everyone on Devilgram's talkin' about her!". Invited to Asmodeus's fashion show in Lesson 32-8.
Lotan
Lotan is a seven-headed sea monster who's Leviathan's second-best friend (after his goldfish Henry). Leviathan wanted to participate with Lotan in RAD's annual Monster Fair event, but instead released the creature into the sea, as he wasn't allowed to keep it. It's mentioned that Lotan ended up creating great havoc and wreaking devastation in the Human World.
Uriel
Uriel is an angel mentioned by Simeon as one of the angels curious about Lucifer. (Hello from the Celestial Realm).
Reaper
The Reaper is a powerful entity that watches over the candles that represent the lives of humans and demons. As of now, the Reaper is genderless, for Solomon doesn't answer Asmodeus's question if they're an attractive man or woman. Solomon is well acquainted with the reaper, for they compete in certain "games" for his soul, but Solomon always wins.
Solomon has stated that the reaper is very aggressive towards him, though this is because they once ate his cooking. They became angry at Beelzebub for accidentally breaking Lucifer's cursed record "Hymn of the Reaper", and reduced his candle significantly. They live in an unknown location in the Devildom that Solomon only knows.
Raphael
Raphael is a high-ranking angel first mentioned in Lesson 44-3. According to Belphegor, he often looked after Michael's needs, no matter how unreasonable, and was meticulous and methodical. He was described to be like a demon in disguise due to his sullen expression.
Back when the brothers were angels, he had an antagonistic relationship with them; he would scold Asmodeus for attending parties, and Lucifer and Mammon would often gang up on them.
The Butcher
The Butcher is a human that appears in the third season. He's first seen when MC and Beelzebub are grocery shopping, and believing they are a couple he gives Beelzebub advice on relationships. MC encounters him again while they're with Mammon, who exclaims they are together much to his surprise.
Lucifer and Diavolo also appear in his shop, and he's stunned by Diavolo's request for dragon meat. He then later met the rest of the brothers while they are shopping, and was shocked again when they began fighting over MC (who wasn't there).
He took his wife and daughter to the theme park Bayside Bonanza World of Wonders, where he ran into MC and Belphegor.