Yuuki is a young man of average height with black hair and dark brown eyes, which are depicted as blue in the anime adaptation. A distinctive feature of his hairstyle is two prominent white strands that emerge from the center of his hairline at his widow’s peak. Initially possessing a typical build, Yuuki’s physique became more toned over time due to regular training and his duties as the 7th Unit’s caretaker. His appearance has garnered attention within the Anti-Demon Corps, with multiple women describing him as either handsome or adorable. Tenka, in particular, once viewed his build as cute and sought to reward him, but as his physique became more defined, she instead developed a desire to be pampered by him.

Although Yuuki is human, activating Kyoka Uzen’s power transforms him into a form resembling a humanoid Shuki. In this state, he wears a collar attached to a chain and takes on various forms depending on the “Learning” and “Lending” of his Slave power, tailored to the woman he is serving at the time.

In his base transformation under Kyoka’s command, Yuuki appears as a smooth, white-skinned, muscular humanoid Shuki with a horned, canine-like face and red tribal markings across his back, shoulders, and chest. His attire consists of wide, samurai-style pants and black leather straps around his wrists.

Yuuki is portrayed as an idealistic, generous, and attentive individual, always willing to assist friends and allies in need. He harbors a strong dissatisfaction with the world’s societal structure, in which men are expected to be subservient to women due to the latter’s ability to gain powers from consuming Mato peaches. Despite his misgivings, Yuuki remains committed to his duties. Driven by a deep desire to become a hero and protect those in danger, he greatly values Kyoka Uzen’s role in enabling him to fulfill that dream, to the point of willingly becoming the 7th Unit’s caretaker.

Upon joining the 7th Unit, Yuuki initially struggled with social interactions, particularly around its female members, as he had little prior experience dealing with women. His awkwardness often placed him in compromising or comedic situations, such as accidentally walking in on members while they were changing. Over time, however, he developed closer bonds with the unit, ranging from camaraderie to genuine friendship, which helped him become more at ease in their presence. His confidence has since grown significantly, to the point where he remains composed even during the unit’s reward sessions. His encounter with Konami further demonstrated that much of his earlier nervousness has dissipated.

Yuuki enjoys his role as caretaker and housekeeper for the unit, a skill set nurtured during his childhood under the guidance of his older sister, Aoba Wakura. His attachment to Aoba borders on the extreme, he has openly expressed a childhood wish to marry her and remains devoted to finding her after her disappearance.

Beneath his respectful and initially timid demeanor lies a latent perverted streak, often revealed during the “rewards” he receives from Kyoka and other masters of her Slave power. Yuuki appears largely unaware of these desires, as seen in Chapter 7 of the manga, where both he and Kyoka were unsettled by the emergence of his masochistic tendencies.

In his Killer Fang form, Yuuki’s personality undergoes a drastic transformation, becoming irrational, bloodthirsty, and indiscriminately violent toward friend and foe alike. This change unsettled even Kyoka, who is typically composed and fearless, prompting her to advise canceling the form immediately. The shift is believed to stem from Ren Yamashiro’s more ruthless and inhuman disposition, which contrasts sharply with the purer wills exhibited by other masters.

Yuuki was raised alongside his older sister, Aoba Wakura, who took an active role in shaping his skills and character from a young age. Aoba’s training often took the form of playful yet rigorous “games,” where she awarded Yuuki high points for tasks performed well and administered wrestling moves as punishment for mistakes. Through this unique upbringing, she instilled in him a strong sense of service and capability, whether for daily life or supporting others.

Six years prior to the events of the series, Aoba disappeared during a catastrophic “Mato Disaster,” leaving Yuuki without any contact or information about her whereabouts. Since her disappearance, he has remained determined to find her.

In the years that followed, Yuuki attended Kaminoge High School, a public institution where the societal norms dictated that male students were responsible for cleaning the school halls before female students arrived. These duties were part of a broader cultural dynamic in which men held subservient roles to women due to the latter’s supernatural advantages from consuming Mato peaches.

As a male, Yuuki is unable to acquire supernatural abilities through the consumption of Mato peaches, unlike women. To compensate, his older sister, Aoba Wakura, trained him extensively from childhood to be capable without relying on such powers both as a self-sufficient individual and as a competent servant for her. This upbringing equipped Yuuki with a range of practical and domestic skills, making him an exceptional caretaker, as well as granting him a foundational proficiency in combat.

Yuuki’s true combat potential emerged after becoming the Slave of Kyoka Uzen through the activation of the 7th Unit Chief’s Peach Blessing. Unlike her previous Slaves, Yuuki’s latent power manifested on an unprecedented scale, making him her most compatible partner. When transformed, Yuuki gains tremendous strength, speed, and durability, enabling him to defeat numerous Shuuki regardless of size in a single strike. His transformation also alters his physical form, granting him the appearance and abilities of a humanoid Shuuki, further enhancing his effectiveness on the battlefield.

The given name Yuuki (優希) can be broken down into the kanji 優 (yū), meaning “gentleness,” “superiority,” or “excellence,” and 希 (ki), meaning “hope” or “rare.” Together, the name can be interpreted as “gentle hope” or “rare excellence.”

The surname Wakura (和倉) consists of 和 (wa), meaning “harmony” or “peace,” and 倉 (kura), meaning “storehouse” or “warehouse.” This combination can be read as “storehouse of harmony” or “keeper of peace.”

When written in kana as わくら ゆうき, the name carries no inherent meaning and serves purely as a phonetic representation.