Reiji has brown hair and brown eyes. When his killing intent shows, his eyes turn green with orange in the center. In the beginning he wears a black button-up t-shirt and a pair of white dress pants. Later, he puts on a black suit with a pink shirt and black dress pants. In the end, he wears grey suit, white shirt shirt, red tie and black dress pants.
Reiji Azuma was a perfectly ordinary tourist from Japan visiting America before he witnessed an Inferno assassination commit a murder. He was able to elude his pursuers long enough for them to realize he had a natural survival instinct that was perfect for an assassin. He had his memory erased through a combination of drugs and hypnotherapy. Reiji was given the choice to join Inferno or die; he joined Inferno.
The name Zwei was given to him by Scythe Master, and Ein , the assassin that was chasing him, was made his trainer and partner. Ein taught Zwei in the ways of an assassin. It didn't take long for Zwei to complete his training. As a test for him, Zwei was ordered to hunt and kill Navy Seal Lieutenant Wallace, who threatened Inferno's discretion. Ein and Zwei then travel to assassinate Don Muchio , a mafia boss. They plan their attack and make their move the next day. Zwei and Ein are sent to assassinate Tony Stone next. Zwei is ordered to break him by killing those close to him- Eva Stone , his wife, and Duke Stone , his son. They then procede to frame Tony Stone and make it look like he killed one of his rival bosses in a drive-by shooting.
As Zwei is giving Ein a ride to her part-time job, Claudia takes Zwei for a ride and a talk. Zwei and Ein are given another mission; they are to back up an assault unit attempting to steal 500 kilograms of cocaine. They return to their hideout to ready themselves for their mission. Zwei gets a phonecall from Lizzie and is given another mission from Claudia: he is to guard Claudia while Lizzie is off on another mission. As Zwei is guarding Claudia, she pulls out Zwei's passport from before he became an assassin. She gives him two choices: stay with inferno as her personal phantom, or return to his past life that was stolen from him.
He takes his passport/his identity and finds that his true name is Reiji Azuma. Reiji struggles with the choices he was given, but Claudia gives him time to think. Reiji then rushes to aid Ein in her mission. He returns to warehouse where he trained to find a shot and bleeding Ein. Ein asks "Did you come here to kill me?" Reiji doesn't know what is going on. Ein passes out and Reiji takes her to their old room in the warehouse. Reiji gets a call from Claudia and she tells him Scythe betrayed Inferno and used Phantom(Ein) to attack one of their shipments and they are both on the run. He is also told he doesn't have any more time to think about his options, and that if he sides with Ein he will be hunted like her. Reiji returns to more important matters and realizes the only thing he can do to help Ein is to remove the bullet himself. After removing the bullet he patches her up and stays with her until she wakes up; this also gives him time to think. He desides to stay with Ein and vows to never let Inferno take her. They leave the warehouse on the run from Inferno.
Reiji, now rejecting his Phantom self Zwei, escapes with Ein while the rest of Inferno gets worked up on finding Scythe Master. Ein had planned to commit suicide by shooting herself as she had no place to call home before Reiji stops her from killing herself. He consoles her and gives her a new name and identity of her own: Eren. Eren encounters Scythe Master in an alley after gunning down an armed man looking for her. Lizzie and Claudia capture Reiji in a parking lot when he is about to hotwire a car. Reiji is subsequently interrogated, being accused of assisting Scythe Master in rebelling against Inferno. Claudia offers Reiji assistance in saving Eren, by releasing his restraints and offering him a pistol for him to use. In return, Reiji promises Claudia that he will take care of Scythe Master.
Reiji in the interrogation room remembers a talk he had with Eren in the car about how she would react to the name Eren. To be able to kill Scythe Master Reiji has to reconnect with his Zwei persona in order to use the latter's assassination skills and power. However he has trouble controlling Zwei and as a result begins acting strangely Claudi sends Zwei and Lizzie alongside a force of men to a wharf in San Francisco, where Scythe Master is being protected by militia of a former acquaintance.But due to inferno men not trusting him Reiji discards all his bullets except one which is for killing Scythe Master.
When he finally makes contact with Scythe Master, Eren is also with him but Reiji realizes that all his efforts to make Eren independent have been undone by Scythe Master. When Lizzie engages in the ensuing fight, Reiji loses track of Scythe Master and Eren.. Reiji get fed up and uses Zwei's true power and is able to track Scythe Master's movements and is able to phantom shift. The strain of using Zwei's power while still mentally rejecting him causes Reiji to go berserk. Eren finds the standoff when Reiji finally corners Scythe Master. When he fires the killing shot Eren at the last second takes the bullet for her master, Reiji looks on in shock as Eren falls into the sea. Reiji drops to his knees, stunned, and Scythe Master shoots him declaring that this was an interesting finale for the battle between him and Ein. All Scythe Master's reinforcements are defeated but Scythe Master himself escapes to Claudia's surprise. As Reiji sinks into the ocean he remembers his promise to make Eren truly smile and live her life as a normal girl. At the end Reiji is seen on a beach lifeless as the sun rises.
- Master Sharpshooter-Reiji is able to accurately fire weapons even in extremely tough conditions.
- Hand to Hand combat expert - Reiji is able to defeat Ein in hand to hand combat and is extremely skilled in using knives.
- Survival instincts- Reiji was chosen by scythe master due to his instincts. He was able to hide in a building for a long period without water or food while being injured.
- Reiji & Eren: Romantic
- Reiji & Cal
- Reiji & Claudia
- Reiji & Lizzie - When Reiji becomes Inferno's new phantom, Lizzie is named his partner. She grows a fondness for Zwei and aids him when he picks up Cal Devens from the Bloodie's turf.
- Reiji & Mio
- Zwei means 'two' in German.