|Height||180 cm (5'11")|
|Weight||67 kg (148 lbs)|
|Division||Contractor, Team 6|
|Previous Division||Soldia, Team 4|
|Rank||甲 Esper of the First Degree|
|Base of Operations||The Agency|
|Likes||Sunday mornings, not working|
|Dislikes||Moving house, being rushed, spicy food, forgetting|
|Hobbies||Sleeping, people watching|
Ryuuhei is a man of medium build with somewhat unkempt brown hair and half-lidded hazel eyes. His uniform consists of the standard longcoat worn with a high collar and loose belt, as well as a partially unbuttoned white shirt underneath. He frequently wears a t-shirt and an unbuttoned casual coat and jeans, giving the appearance of any casual passerby on the street, instead of wearing uniforms like many of his fellow Vespers. His appearance echoes his personality and thus he often presents himself in an unkempt, uncaring fashion, slouching during important meetings or sleeping in unsuitable places.
His preferred weapon is Gina, a dark silver revolver that is capable of changing form, although he carries an Athamé called Kao no Nai that he rarely uses. He bears the mask of his deceased host.
Ryuuhei is invariably described as lazy, uncaring, arrogant, and disagreeable by both friends and enemies. He is also extremely intelligent and shrewd and is an excellent judge of character, able to manipulate others into doing his will simply by getting into their heads without them realizing. This is all done without any sort of power. He is a master of working incognito, something he describes his partner Zeno as incapable of ever learning. Despite understanding the subtleties of working incognito, he is very not subtle in his relationships, as Phaedra points out. He has many enemies, partially because of his tactless way of speaking without filter. However, it is frequently implied that he does this on purpose to rile others.
Although he is incredibly lazy, it is heavily implied that he has genuine sleep issues brought about by his connections with NUE, and it is shown that many Vespers suffer from some amount of insomnia brought about by their ability to use power. Ryuuhei is frequently shown to be up at night and napping during the day. At one point he is dubbed a vampire by Fuyuki. Similarly, he cannot eat human foods, but frequently visits restaurants and places where these things are served. It is implied that he is a masochist.
Despite his lazy appearance, however, it is shown that he is incredibly strong-willed, which is one of the reasons for his survival among so many failed experiments. He is ruthless and competitive, though not nearly as competitive as his partner Zeno, since he "just doesn't care."
His goal of taking down the Agency did not come until he received Gina's power, and consequently, some amount of her will.
- Ryuuhei's relationship with Madoka is strained, but often humorous. They are usually in competition with one another, even when their aims are the same; they somehow manage to fight over things they even agreed over previously. Ryuuhei finds Madoka to be too vague and misleading, although Madoka accuses him of exactly the same thing.
- Zeno Arakawa - Ryuuhei frequently gets into spats with his partner, who is the exact opposite of him in almost every aspect. Despite their frequent opposition, they make good partners, particularly on missions or on the battlefield. Their partnership in the office is a complete nightmare, with Ryuuhei forgetting to do almost all the work and shouldering it onto Zeno. As Phaedra notes, they are like yin and yang.
- Phaedra Vacanti - She is Ryuuhei's unofficial work partner and his best friend. They fight viciously both in private and in public, but they defend one another to the same degree; Zeno says they're inseparable. Phaedra rescued him from despair after his turning, and they've worked together ever since.
- Gen'ya - Ryuuhei harbors an intense dislike of Gen'ya "for almost no reason at all." When Gen'ya first shows up to prevent Isasu from slaughtering them, Ryuuhei is immediately suspicious of his motives. Even after Gen'ya takes Fuyuki under his wing, Ryuuhei does not like Gen'ya. Gen'ya's cool, impenetrable personality ruffles his feathers, and Ryuuhei seems to interpret his aloofness as being better-than-thou, although it has not proven whether Vespers or Sealed half-demons are stronger. Despite Ryuuhei taking all of Gen'ya's remarks as challenges, Gen'ya never rises to the occasion.
Ryuuhei was an orphan and a natural Esper who was taken in by NUE at a young age. He subsisted on very little and apparently endured horrifying experiments, including the repeated destruction and rebuilding of his soul, as they tried to merge human soul matter with the Shigyoku of the angels. He was forced to live in what was essentially a cage for much of his childhood. Out of the hundreds of experiments in Group 23, he was the only survivor. He was the second successful Vesper creation, after A-1049.
Ryuuhei arrives at the shop while on a mission to target a powerful Ochigami in the area. This hunt brings him to Fuyuki's place of work, where his target is another customer. Chaos ensues as the mission goes awry, and unbeknownst to him, Fuyuki awakens his powers.
Ryuuhei immediately notes that Fuyuki has some kind of ESP capability after the boy points out his number, which only those with Sight can see.
Ryuuhei is a specialist in Kūdō-based attacks. He avoids using his Athamé at all costs and prefers using his gun, Gina. He is also proficient in Jidō, though he usually uses these spells to slack off.