Ajuka Beelzebub, formerly known as Ajuka Astaroth, is the current leader of the Underworld and the only Satan left after the events of 666. He is the Chief Advisor for the Technology Department and the creator of the Evil Pieces system and the Rating Game.
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 is also quiet possess 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' enemies 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 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.
He first appears in Volume 5 along with the other Satans during the opening ceremony for the Young Devils Gathering, although he was silent throughout.
In Volume 8, he participated in Issei and Rias' ceremony at the Ruins of Connection, where he acted as Satan Blue and tested them on the history of the house of Gremory and general knowledge of the Underworld. After the ceremony, he decided to have a look at Issei's Evil Pieces after learning that the original program written by him was overwritten by a different code, which he speculates to be the effects of the Juggernaut Drive, but was in a messy state that could cause the Evil Pieces to malfunction. He then rewrote the code written in Issei's Evil Pieces to allow his Evil Pieces to adapt to the power of the Red Dragon Emperor. Before going home after altering Issei's Evil Pieces, he asked if Issei is interested in playing in a new "game" he developed, which Issei refused.
In Volume 12, Ajuka was in the human world preparing a method to defeat the Jabberwocky and Bandersnatch that are attacking the Underworld. Rias and the others came to visit him, hoping that he would check on Issei's Evil Pieces wanting to know if Issei is still alive. The meeting was interrupted by the arrival of Siegfried and the Old Satan Faction who attempted to form an alliance with him. It was also revealed that the "game" he mentioned in Volume 8 involved thwarting the Khaos Brigade. However, he rejected their offer and finished off the Old Satan Faction with his Kankara Formula, leaving Siegfried to the Gremory Team. He then checked on Issei's Evil Pieces and was interested to find out that four of his eight Pawn pieces evolved into Mutation Pieces, which he speculates to represent the Triaina and Cardinal Crimson Promotion armors. After checking the Evil Pieces, he gives assurance to the Gremory team that Issei's soul is alive and still has his Sacred Gear with him while telling the team that the Evil Pieces can still be used on Issei.
The Gremory group, Sitri group, Irina, and Azazel, went to a dimension owned by Ajuka in Volume 20. They did so as they had received news that both Riser and Ravel Phenex are in his custody after the disastrous Rating Game between Riser and the Emperor, Diehauser Belial. Team (D×D) were sent to Ajuka's dimension, "Another World", where Ajuka updated them on Riser and Ravel's condition, telling them that Ravel was still with him. He then filled them in on the reason why he had the Phenex siblings in his custody and explained about the King Piece along with the darkness of the Rating Game. When asked why it only occurred in Riser's match, Ajuka simply told them that they would understand in time. After that, Azazel and Ajuka had a conversation about the two remaining Longinus, Innovate Clear and Telos Karma. Ajuka received a communication call, then told Team D×D to return because Ophis had been attacked by an Evil Dragon. Later, after the invasion of Agreas, Ajuka and Shiva talk over a board game in a private resort in the Fallen Angel territory of the Underworld, all while watching the awakening of 666. Ajuka explains that he is meeting with Shiva to keep him from interfering with Sirzechs and to keep him from making trouble during the unfolding events. After Ajuka explains his theory about Trihexa, Shiva laughs, telling him that he now understands why other mythologies fear Ajuka even more so than Sirzechs, but also tells him that he is not afraid of Ajuka. Shiva then asked if he is doing what Sirzechs did to Hades during the Jabberwocky incident, and how important his friendship with Sirzechs is. Ajuka simply smiles and tells Shiva if he becomes Sirzechs' enemy, he will become his enemy. They then sit back and watch Trihexa.
In Volume 21, Ajuka ask Shiva if it was alright for him to stay behind, as he once accepted Azazel's proposal when Trihexa tried to invade the other world, Shiva would appear to stop it. Shiva says he was insisted that he stay and become the stopping force by Brahma and Vinshuu. Ajuka decided to remain as a Satan until Sirzechs returns and bearing the duties of his friend's duties, as well of Falbium's duties.
In Volume 22, Ajuka attended Issei's promotion ceremony and starts reading the certificate and starts making Issei a High-class devil. At the altar, Ajuka tells Issei to stand in front of the monument and received his Evil Pieces. After the ceremony, Ajuka brought Shiva and the young prince of Asuras Mahabali who they been wanting to meet Issei. After a small conversation between Issei and Shiva, Shiva asked Ajuka if he remembers the condition Azazel gave him. When Shiva asked Issei to join his army for the war against Indra, this shocked Ajuka and protested to Shiva, but was stopped by him, telling Ajuka that Indra is increasing his forces to defeat him and gathering notable fighters such as Cao Cao and Sun Wukong and there's a high chance he might take in the Azazel Cup.
Powers & AbilitiesEdit
Immense Demonic Power: As the current Beelzebub, Ajuka is one of the most powerful Devils in the Underworld. In fact he, along with Sirzechs Lucifer and Rizevim Livan Lucifer, is one of the three Devils who are considered Super Devils, with their powers and abilities far exceeding even that of the Four Original Satans, rivaling that of some of the more powerful gods. This was shown when he easily disposed of the Devils of the Old Satan Faction which consisted of High-Class and Ultimate-Class Devils (who enhanced themselves through unknown means), all while sitting. Zeoticus Gremory has stated that Ajuka and Sirzechs' immense power made it so that there was no position worthy for them besides being Satans.
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 and different magic calculations, it is particularly shown when he formed and developed anti-spells and method against the Jabberwocky and Bandersnatch that are attacking the Underworld during the events of Volume 12. Ajuka and his servants created a different magic-circle technique problems that work on the rampaging monsters.
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): Ajuka's specialized move which has the ability to control all phenomenon using equations and formulas and modify it to make it into a special move of his own. Ajuka can take control of his enemies' demonic power attacks, change their shape, direction, and also increase their power.
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 anytime. 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.
- 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.