Apocalypse AnswerArms is the third upgraded form of the Scale Mail after Issei pilots his familiar Ryuuteimaru, who manifests Great Red’s power due to him being Issei's familiar thus allowing him to make use of Great Red's aura in Issei's body.
In True Volume 3, Issei went together with Rias and Ravel to visit the Grigori establishment to meet up with Shemhazai and check up on Ryuuteimaru which had undergone a metamorphosis and wrapped itself in a red cocoon, changing from its giant ship form to a new smaller form. Seekvaira Agares, who was one of the leaders of the Grigori Research Team of Ryuuteimaru, explained that Ryuuteimaru had changed its form from a flying ship to a flying unit and added new weapons to itself as well as a hole which appeared to be a piloting control space. Ophis later appeared together with Lilith at the establishment to explain that Ryuuteimaru’s transformation is the result of Ryuuteimaru mixing together Issei's power, Ophis's power and Great Red's power as a result of being Issei's Familiar.
During the fight against Tartarus, Ophis and Lilith teleported to the battlefield, bringing along Seekvaira and the evolved Ryuuteimaru, which had almost completed its metamorphosis. Issei combined with Ryuuteimaru which enabled them to achieve AxA. Using this form and Ddraig's manifestation, Issei was able to defeat Tartarus.
Ophis speculated that the cause of this transformation is that Ryuuteimaru is evolving in anticipation for future threats, and Azazel and Ajuka discussed with each other that Ryuuteimaru had a will of its own and they never erased its memory about the events of High School DxD EX, implying that its evolution is the result of it preparing for the invasion of the [Underworld Lifeforms] from Evie Etoulde.
The power of this form is so great that it could easily overwhelm Tartarus, a Primordial God in Greek mythology. It has the power to destroy the entire planet with its destructive power. Although it is currently in an imperfect state, the power is so colossal that it could be capable of breaking the whole planet with one attack, and is classified among the highest class of firepower and defense in the world. Because of the weapons that were installed in Ryuuteimaru, Issei has gained new abilities of this form, most of which are yet to be revealed.
- Revelation Barrier (レベレーション バリアー, Reberēshon Bariā): Creates a stronger barrier around the body and is powerful enough to withstand attacks from Gods such as Tartarus.
- Revelation Blade (レベレーション ブレード, Reberēshon Burēdo): With four arms of his Apocalypse AnswerArms form, each of the arms carries aura blades known as Apocalypse Ascalon (アポカリュプス・アスカロン, Apokaryupusu Asukaron), which are powerful enough to easily cut through Tartarus’ tentacles.
- Revelation All-Range Blaster (レベレーション オールレンジ ブラスター, Reberēshon Ōrurenji Burasutā): Similar to Cardinal Crimson Promotion and Diabolos Dragon God, Apocalypse AnswerArms has many cannons to fire powerful blasts of aura strong enough to destroy Tartarus’ magic barriers like paper and destroy almost half of his body, even as Issei held back his power. The blast of destructive energy is so powerful it can alter the environment and is strong enough to destroy the artificial space created by Dimension Lost. Issei stated that the blast is comparable to several Infinity Blaster blast attacks combined, even when holding back its power.
- Due to the large aura consumption and unstable nature of AxA when it manifested, Yuuto Kiba compared it to the initial state Cardinal Crimson Promotion upon its manifestation.
- Apocalypse AnswerArms is modeled after the RX-78GP03 Gundam "Dendrobium".
- Perhaps, the word “AnswerArms” is combination of words “answer” and “firearms”.