Johannes Kleeman was born in Obihiro, Hokkaido, as part of White Group 07 in the fifteenth Hybrid Birth Project. His mother was a Chinese devil, and his father was a German human. Created specifically for ONLO’s research into hybrid abilities and traits, he was placed under the organization’s care from birth and never held a legal parental relationship with either parent.

During his upbringing, Lee was subjected to extensive testing to evaluate his ReMI (insufficient transformation) status and regenerative capabilities. These experiments often involved inflicting injuries, administering blood, and recording the healing process. Due to the high value of his test results, Lee was kept under constant guard and isolated in a private room. Books became his only source of entertainment and education, granting him broad knowledge of the outside world. Over time, his cooperation with researchers led to the success of his “single eye” transformation. Among all he learned, the concept of “the endless sky” fascinated him most.

At around twenty years old, Lee found an opportunity to escape through a lapse in facility security, intending only to see the open sky before returning. However, Midori Anzai, an ONLO devil researcher, advised him to flee permanently, warning that he would never be allowed outside again if he returned. She provided him with essential funds and encouraged him to find a true home, revealing his real name Johannes Kleeman before parting.

Following his escape, Lee traveled across Japan, evading repeated attempts to recapture him. His transient lifestyle brought him into contact with various individuals who offered him shelter and blood, including Dr. Feng Jing, with whom he became well acquainted. From this time onward, he began using the alias “Hans Lee.”

Lee is a tall young man of average build, often regarded as handsome. He has long, straight silver hair white in the anime adaptation—that reaches his upper back and typically drapes over his left eye. At times, he wears his hair in a ponytail at Tsukasa’s suggestion. His eyes are blue, though his left eye is permanently in a transformed state: the sclera is red and the iris a golden yellow. This condition results from his routine blood consumption, which restores vision in that eye but also triggers partial transformation.

Lee’s clothing style favors comfort, with loose-fitting garments such as hoodies being a common choice. He has also been seen wearing a cross necklace resembling the design of Yuuki Anzai’s ring.

Following the series’ timeskip, Lee initially appeared with shorter, unevenly cut hair, a result of trimming it himself along with mantels, hoodies, and other casual attire. Upon becoming the public face of a devil protection campaign, his appearance shifted to reflect the style of Queen and her associates, including heavy eyeliner, earrings, and a high, messy ponytail with slicked-back bangs.

After stepping down from his role as a poster figure, Lee reverted to his earlier style from before the nine-month timeskip, though his hair remained slightly shorter than before.

Lee is portrayed as an eccentric and free-spirited individual, often seen eating regardless of the situation even in moments of danger. He has a laid-back disposition paired with a blunt, straightforward manner, unafraid to speak openly or confront others directly. Quick-witted and perceptive, he can read between the lines and identify when something is amiss, though his remarks sometimes blur the line between sincerity and humor. Energetic and curious by nature, he exudes a bright and approachable presence.

Despite being guarded about his past, Lee makes no effort to conceal his identity as a hybrid. He lives according to his own pace and values, largely disregarding the opinions of others. This self-directed lifestyle, however, has at times made him insensitive to the feelings of those around him. His tendency to judge situations solely by his own standards without weighing emotional impact began to soften after spending time with the F Squad, where he recognized the shortcomings of his approach. In personality, he is often seen as the opposite of Yuuki Anzai, with whom he contrasts sharply.

While generally lighthearted and humorous, Lee is capable of adopting a serious, intimidating, and confrontational stance when he deems it necessary. Level-headed and difficult to manipulate, he refuses to justify harmful actions on the basis of personal hardship. His moral compass is rooted in his own beliefs rather than societal norms, and though often regarded as a hero for rescuing people from devil hunters earning him the nickname “The Silver Wolf”, he insists his interventions are incidental, claiming he was merely “out for a walk” when they occurred.

Confident in his abilities and completely in control of his hybrid nature, Lee possesses extensive knowledge of devils, hybrids, and himself, though he expresses little interest in broader racial conflicts. He is, however, intrigued by the interactions and behaviors of humans and devils, particularly the dynamic between Tsukasa Taira and Yuuki Anzai.

Lee values freedom deeply, shaped by his isolated upbringing, and views the sky as the ultimate symbol of liberty and home. While he initially professes little trust in familial bonds and denies being part of the “large family” formed by the F Squad and their allies, he gradually comes to see the group especially Tsukasa and Yuuki as his own family. This realization cements his sense of belonging within the F Squad and influences many of his later choices.

Fighting Skills and Strength
Lee is an exceptionally skilled hand-to-hand combatant, capable of matching the speed and strength of transformed devils even without undergoing transformation himself. His fighting style incorporates a mix of kicks, throws, holds, and strikes, allowing him to subdue multiple opponents in quick succession. Possessing high stamina, speed, and agility, he is able to evade attacks with precision while delivering counterattacks effectively.

Transformation and Healing
Through the disciplined practice of consuming small, measured doses of blood twice daily, Lee has developed near-perfect control over his bloodlust. While he can transform upon exposure to or consumption of blood, he retains full mental clarity during the process. His transformation is limited to his left eye, which takes on a red sclera and golden iris, while the rest of his body remains unchanged, an advantage unique to his hybrid physiology.

Lee’s in-depth understanding of his own biology, as well as that of devils and hybrids, enables him to gauge exactly how much blood is required to heal specific injuries and to sustain his vision and physical performance. His baseline bloodlust is notably low, and when he senses it beginning to rise, he has developed personal methods to suppress it, acknowledging the connection between bloodlust and a devil’s sexual drive.

Lee is introduced as a mysterious hybrid who has evaded ONLO’s control for several years, living under the alias Hans Lee. His arrival in Tokyo and subsequent encounters with Yuuki Anzai and Tsukasa Taira bring him into contact with the F Squad, where his unique perspective, combat skills, and extensive knowledge of hybrids become valuable assets.

Initially operating as an outsider, Lee assists the squad in several operations, particularly in matters involving devil hunters and the management of bloodlust. His calm, level-headed approach contrasts with Anzai’s more emotionally driven nature, allowing him to offer strategic insight and blunt advice, even if it occasionally causes friction.

Lee also serves as a foil to Anzai in exploring the series’ themes of self-acceptance and coexistence between humans and devils. While Anzai struggles with self-identity, Lee displays confidence and control over his hybrid nature, prompting moments of reflection and growth in other characters.

Midway through the story, Lee temporarily becomes the public face of a devil-protection movement, leveraging his appearance and charisma to promote awareness and cooperation between species. Though his role as a “poster child” eventually ends, the experience deepens his understanding of belonging and solidifies his bond with the F Squad, ultimately influencing his decision to remain with them and consider them his true home.