|“||It’s good having a mysterious atmosphere because it seems devilish. Oh, sorry. Nice to meet you, Sekiryuutei-dono. I have heard rumours about you.||”|
Ajuka Beelzebub, formerly known as Ajuka Astaroth, is the current leader of the Underworld and the only Satan left after the events of the Evil Dragon War. He is the Chief Advisor for the Technology Department and the creator of the Evil Pieces system and the Rating Game. He is the former heir to the Astaroth Clan and comes from the branch family of the Astaroth Clan.
Ajuka is a bewitchingly beautiful and attractive young man appearing in his early twenties, with light blue eyes and green hair that is slicked back. He has a mysterious aura around him which he claims makes him seem devilish.
Ajuka is a rare person among Devils who “creates”, preferring to create new things and claiming that it is one of his hobbies. Ajuka, however, doesn’t care much about the role as a Satan, focusing more on his hobby over his job, and also has a easy going nature like his fellow Satans. Despite this, Ajuka isn't irresponsible and will fulfill his role as a Satan when required, proven when he kills the Devils of the Old Satan Faction and creating a method to defeat the Jabberwocky and Bandersnatch to protect the Underworld.
He also possesses a dry sense of humor towards his enemies, particularly from the Old Satan Faction, as he called "praises" all discrimination and criticizes that the Devils from the Old Satan Faction throw at him, and tends to mocks his enemies if he deems them worthless.
Ajuka highly values his friendship with Sirzechs, Serafall and Falbium. According to him, whoever becomes Sirezchs' enemy will also become his. He even upright told Shiva, an immensely powerful God to not hinder Sirzechs to which Shiva just simply laughed. After his fellow Satans sealed themselves away in the Isolation Barrier with Trihexa, Ajuka resolved to shoulder their respective duties and watch over the Devils in their place on account of their friendship. He is still a kind and caring person, as he helps Issei and the Gremory team with their various problems.
A member of a branch family of the Astaroth clan, Ajuka is Sirzechs Lucifer's childhood friend and rival. Like Sirzechs, he was also an ace of the Anti-Satan Faction and became a Satan after the conflict between the Old Satan Faction and Anti Satan Faction came to an end. Sometime after being a Satan, Ajuka created the Evil Piece system to help replenish the number of Devils which eventually lead to the creation of the Rating Game.
Powers & Abilities
Immense Demonic Power: As the current Beelzebub, Ajuka is one of the most powerful devils in the Underworld. In fact, he, Sirzechs and Rizevim are three Devils considered Super Devils with their powers and abilities exceeding that of the original Four Great Satans and rivaling some of the more powerful gods. This was shown when he easily disposed of the Old Satan Faction devils, which consisted of High-Class and Ultimate-Class Devils (who enhanced themselves through unknown means), all while sitting. Zeoticus has stated that Ajuka and Sirzechs' immense power made it so that there was no position worthy for them besides being Satans.
- Calculation Demonic Power: Due to his interest in calculations, Ajuka had developed his demonic powers to specialize in calculations. His Demonic Power is so unique that among all the Devils, only Ajuka's Demonic Power specializes in creation.
- Kankara Formula (覇軍の方程式, Kankarā Fōmyura): Also known as Equation of Military Supremacy, it is Ajuka's specialized move which has the ability to control all phenomenon using equations and formulas. With it, he has shown the ability to take control of his enemies' demonic power attacks, change their shape, direction, and also increase their power.
Master Magician: Ajuka is a genius in researching demonic magic spells particularly to those created by the original Satans. In his youth, he shown to have known many different magic calculations, it is particularly shown when he formed and developed anti-spells and methods against the Jabberwocky and Bandersnatch that are attacking the Underworld during the events of Volume 12. Ajuka and his servants created different magic-circle technique problems that worked on the rampaging monsters.
Genius Intellect: Ajuka is an extremely rare genius described as possessing such knowledge from a young age that no one in the Underworld other than Azazel could compete with him. His immense intellect has contributed to his skills as a researcher, inventor, and tactician with Sirzechs stating he was irreplaceable.
- Master Tactician: Alongside Falbium, Ajuka is credited as a tactician of the highest caliber to the point of being able to predict figure events, which is the reason that he's feared around other mythologies more than even Sirzechs. Following the other Satans's departure inside the Isolation Barrier Field, Falbium, the Underworld's greatest strategist, acknowledged Ajuka's tactical genius, stating that Ajuka is a suitable replacement for him in handling strategy coordination.
- Master Inventor: Due to liking calculations and creating things, Ajuka has became a successful inventor, as well as the Chief Advisor of the Technology Department. His most notable achievement being the Evil Piece System, which can create reincarnated devils from another species aside from gods. As such, he's able to modify Evil Pieces, letting Issei promote anywhere without permission and turning a normal ones into Mutation Pieces. He noted whereas Azazel loved creating something from another base, he, on the other hand, loved creating something from nothing. He received praise from Diehauser who stated his talent as an inventor were too extraordinary as he invented the King Piece which could abnormally enhanced a Devil's demonic power which the Great King Faction had used to monopolized the Rating Games before it was confiscated.
Flight: As a pure-blooded devil, Ajuka can fly using his Devil wings.
Being the Chief Advisor of the Technology Department of the Underworld, Ajuka has created many inventions beneficial to it. The notable ones are below:
- Evil Pieces: The system used by devils today that allows for easier repopulation; where the High-Class Devils reincarnate other beings, notably humans, especially one with Sacred Gears, into Devils to create a small group of individuals with high power rather than an army of small power.
- Evil Pieces Scanner: In Volume 12, Ajuka showed a chess board that scans the Evil Pieces placed on it for any abnormalities when the Occult Research Club visited him to find out about Issei's status through his Evil Pieces.
- King Pieces: Rare Evil Pieces, which were created in the early days of the Rating Games by Ajuka but discontinued in production due to the potential danger from evil people misusing them. Originally only 9 were created and snatched away when the Old Devils obtained the commercial rights for the Rating Games. Ajuka managed to reclaim all of them after their existence was exposed by Diehauser Belial.
- He claims that the only reason he became a Satan was because Sirzechs became one himself.
- Ajuka was considered for the position of Lucifer along with his rival, Sirzechs, after the devil civil war due to their immense strength and status as Super Devils. However Sirzechs was chosen for the position due to being better at gathering people than Ajuka.
- His name is made from combining the first syllable of the names of three protagonists from the first three Gundam TV series (Mobile Suit Gundam 0079, Mobile Suit Gundam Z, and Mobile Suit Gundam ZZ). Amuro Ray + Judau Ashita + Kamille Bidan = Ajuka.
- The only known member of Ajuka's peerage is the "King Snake of the Realm of the Dead", Falak. 
- Falak in Arabian legend is the powerful serpent that lives under the Realm of Fire.
- Ajuka is one of the two known Devils to be placed among the ranks of the Top 10 "Strongest Beings in the World", the other being Sirzechs.
- "Ajuka Stadium", one of the many stadiums in the Azazel Cup was named in Ajuka's honor.
- Ajuka's demonic powers which specializes in creation serves as the perfect contrast to Sirzechs' demonic powers which specializes in destruction.
- Ajuka’s smartphone game is called Belzebut.