|“||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. 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. He is still a kind and caring person, as he helps Issei and the Gremory team from 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: Even at a young age, Ajuka already possess such knowledge that no one (other than Azazel) who can compete him in the Underworld, a rare case when it comes to/among the Devils. His knowledge gives him a high degree of advantages, in many ways especially when it comes to calculations, magics, and equipment.
- Master Tactician: Ajuka is credited as a genius, a tactician of the highest class. His ability to predict future events was noted to be the reason that Ajuka is even more feared by other mythologies than Sirzechs is.
- Master Inventor: Due to his liking of calculations, Ajuka became a successful inventor with the fact that he created the Evil Pieces system that helped repopulate the devils and eventually the Rating Game. He even became the Chief Advisor for the Technology Department. Ajuka also modified Issei's Evil Pieces to allow the latter the ability to promote anywhere at any time. After the modification, Issei had mentioned that he could work very well with Azazel in inventing though Ajuka discounted this idea basing it on that Azazel likes to create something from another base while he himself likes to create something from nothing.
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.