Ryuuteimaru initially bears a resemblance to a toy boat, but will eventually change in size and shape along with Issei's growth.
By Volume 17, Ryuuteimaru was large enough to allow Asia and Rossweisse to ride on it around the battlefield.
As of Volume 22, Ryuuteimaru has grown into an enormous flying ship adorned with the design of a dragon, capable of carrying more than several people.
As of True Volume 3, Ryuuteimaru underwent a metamorphasis, becoming Apocalypse AnswerArms.
Ryuuteimaru is one of the legendary Skíðblaðnir ships that were made by the tribe called Ívaldi who also created Thor's Mjölnir. Supposedly, very few of these ships were created.
Powers & Abilities
Growth: As a Skíðblaðnir, Ryuuteimaru will grow and evolve into different forms using the aura and imagination of its master as its source. In Volume 17, it turned into a boat large enough for Asia and Rossweisse; in Volume 22, it turned into an enormous flying ship with dragon motifs; and in True Volume 3, using Great Red's aura that was still dormant in Issei, it turned into a powerful mobile armored base.
Immense Strength: Despite its small size, it can still fly while carrying its master. Issei states that it has amazing horsepower and strength, which was demonstrated when it was able to carry him during the battle with the Stray Magicians. In Volume 22, it grew to an enormous ship with a dragon exterior capable of carrying around Issei and his entire team. According to Rias' words, Ryuuteimaru in AxA is able to destroy a planet just by one shot.
Future Predict: Ryuuteimaru's growth helped it gain the ability to predict future threats.
Flight: Ryuuteimaru is able to hover and levitate itself.
Apocalypse AnswerArms (AxA)
Through using Great Red's power, Ryuuteimaru is able to transform into a powerful mobile armored base, which Issei is able to merge with and pilot, allowing him to utilize the power he attained from Great Red. Apocalypse AnswerArms' power was great enough that it could overwhelm Tartarus, a Primordial Greek God, and can even destroy the world if Issei misused its destructive power. Due to all the weapons installed in Ryuuteimaru, it has attained additional abilities in this form.
- 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 an aura blade known as Apocalypse Ascalon (アポカリュプス・アスカロン, Apokaryupusu Asukaron), which can easily cut through anything like 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 both Cardinal Crimson Promotion and Diabolos Dragon God, Apocalypse AnswerArms has many cannons to fire powerful blasts of aura that can destroy Tartarus’ magic barriers like paper and destroys 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 states that the blast is comparable to several Infinity Blaster's blast attacks combined.
- Issei named Ryuuteimaru using the Ryuutei (龍帝, Dragon Emperor) apart of namesake as the Sekiryuutei and maru (丸, circle), which was used to name ships in Japan.
- So its full name is Dragon Emperor Circle.
- According to Ichiei Ichibumi’s words, Ryuuteimaru still has unrevealed weapons which will be introduced in the future.