Prisoner D-431

Prisoner D-431 is an unnamed minor antagonist who only appears in the Begleiter pilot chapter. He is a shapeshifter, and appears as a prisoner in Hohburg Fortress, the eighth area prison, where he escapes and attempts to kill Ayanami in a suicide bombing, but after Yukinami intervenes and saves Ayanami, he only manages to kill himself.

Physical appearance
Prisoner D-431's true form appears as a man of average height with a thin, long-limbed frame covered in scars from past battles. His face is triangular, with small, wide-spaced, beady eyes, a short mop of light hair, and a wide nose.

Clothing
He wears tight-fitting, knee-length, black trousers.

Personality
Prisoner D-431 appears as ruthless and cruel as he kills anyone who gets in his way, ignoring age or profession. He appears ambitious, as he stopped at nothing to achieve his goal, even if it meant killing himself. He is also sly and intelligent, as he was able to devise a plan that helped him escape, and trick almost everybody into believing he was the person he was impersonating.

Abilities and Attributes
Prisoner D-431 is a shapeshifter, which means he is able to change his physical appearance freely, through contact with his mouth. This ability also appears to cover the voice of the person he is impersonating, as his ruse was not given away when he spoke. He is able to "stock up on faces", meaning he is able to store faces for later impersonation, though it is unknown what the limit is, but can only use each face for 30 minutes. It is unknown if he can or cannot shapeshift clothes too, as when he first demonstrated his ability he was seen without the guard's clothes, but when he impersonated Yukinami, he was seen with an identical cadet uniform, despite Yukinami being the only cadet around, and he was still wearing the uniform.

Hand-to-hand combat
Prisoner D-431 appears to be an able swordsman as he was easily able to take down multiple armed guards in a relatively short space of time.

History
It is possible that Prisoner D-431 is a native of the kingdom of Raggs as he had said that Ayanami was responsible for the death of his people, although this could be debated as Barsburg has claimed many other kingdoms. At one point he committed a crime and was imprisoned in Hohburg Fortress, possibly the killing of Barsburg soldiers, and vowed to take revenge against Ayanami.

Escape
He first appears trapped in a cell in the eighth area prison when a guard approaches him. Prisoner D-431 grabs his collar through the bars and licks his face. When the guard reels back in shock, the prisoner explains that he had a fly on his face. He later impersonates the guard whose face he licked and uses this disguise to trick another guard to release him, pretending he is the real guard and that the prisoner had locked him in his cell. When the guard is fooled and opens the cell, Prisoner D-431 kills him and then impersonates him and steals his clothes. He then makes his way through Hohburg to the fifth block, killing anyone who gets in his way.

Battling Yukinami
Meanwhile, Yukinami having gotten lost while retrieving documents for Ayanami stumbles across Prisoner D-431 (in another disguise) and reveals his post as Ayanami's begleiter to him. When Yukinami turns, the prisoner attacks him but Yukinami dodges the blow.

Battling Ayanami
As Ayanami waits in Raphael's tower, Yukinami appears before him and tells him that he managed to capture the prisoner and deliver him to the guards. Upon hearing this, all the guards in the room leave, leaving Yukinami alone with Ayanami and Hyuuga. However another Yukinami appears and claims to be the real one, and the two Yukinamis fight. Just as one Yukinami has the other pinned to the floor, about to deliver a fatal blow, Ayanami severs his arm with his sword, revealing him to be the prisoner in disguise, Ayanami recognising him because he doesn't have "the eyes of a puppy" like the real Yukinami does.

Death
As Prisoner D-431 lunges at Ayanami, Hyuuga steps between them and slices the prisoner across the chest. Ayanami then orders him to be taken back to his cell for interrogation, but Prisoner D-431 reveals a bomb concealed within his clothing. He detonates the bomb with the intention of killing Ayanami along with himself, but Yukinami intervenes and teleports Ayanami, Hyuuga and himself to the top of another tower, saving them and meaning the prisoner only managed to kill himself.

Trivia

 * He is the only pilot chapter-only character in the series.