Tamaki Anzai met and fell in love with a human woman, Miho Kaneda, during their university years, where they both studied architecture. The two were partners for a decade, sharing a deep emotional bond. Their relationship took a tragic turn when Miho was assaulted by five men while walking alone at night. Devastated, she fell into depression and eventually took her own life. The perpetrators were convicted and sentenced to six years in prison but were released after serving five.

Driven by grief and a desire for revenge, Tamaki tracked down and killed the five men responsible. However, after the killings, he lost control and went on a violent rampage, murdering ten additional people, including innocent bystanders and family members of the assailants. This mass killing resulted in his conviction and a death sentence for the murders of fifteen people.

Tamaki’s dependence on blood intensified after consuming the blood of his victims, making him an ideal subject for ONLO’s research into blood addiction in devils. ONLO secretly arranged to have him transferred into their custody, avoiding the death penalty in exchange for his participation as a research subject. He was also selected as a sperm donor for the fifteenth term of the Hybrid Birth Project.

Haunted by memories of Miho’s death and the massacre, Tamaki spent years in solitary confinement, refusing to speak and avoiding interaction with others. Drinking blood triggered particularly vivid and painful flashbacks. His isolation began to change when researcher Midori Sako initiated dialogue sessions with him. While he could not speak, Tamaki used a whiteboard to communicate, and the two gradually learned Japanese Sign Language to facilitate conversation. Their bond deepened over time, and Midori encouraged him to work on a project, constructing a scale model of a dream house he had once envisioned building for Miho. Completing the model allowed Tamaki to finally release some of his grief.

When the Hybrid Birth Project pairs were assigned, Tamaki was initially partnered with Ibuki Takeya. He felt indifferent toward the arrangement, viewing it as repayment to ONLO for sparing his life. However, when Midori asked how he would feel if she were to be the mother, he was taken aback. The thought caused him stress, resulting in a fever that led to hospitalization. During her visit, Midori explained that the process would involve artificial insemination, which relieved Tamaki, who believed physical intimacy with a human would be impossible. In that moment, he confessed his preference for Midori as the mother, and they admitted their feelings for one another.

ONLO granted permission under the condition that Ibuki serve as a surrogate to avoid damaging the organization’s reputation by directly associating a researcher and a convicted mass murderer in reproduction. Ibuki consented, and the couple’s son, Yuuki Anzai, was born. Due to Yuuki’s status as part of the Hybrid Project, ONLO retained full custody, and Tamaki and Midori never had a legal parent-child relationship with him. Nonetheless, Tamaki held a deep love for his son.

Despite their unusual circumstances, Tamaki and Midori sought ways to live together, sometimes involving Midori carrying a firearm and tranquilizers, or ensuring they were never alone without safeguards. Eventually, they married.

Because Tamaki’s crimes were considered a rare and extreme case in devil history, detectives and prosecutors often visited him for training purposes. One such visitor was detective Kirio Kikuhara, who took an interest in Tamaki, seeing similarities in their backgrounds as killers. However, Tamaki, unlike Kikuhara, had moved beyond hatred and hoped someone would eventually “save” him. Dissatisfied with Tamaki’s responses, Kikuhara turned his attention to Yuuki, leading the boy to the underground prison where Tamaki was held. There, he revealed Yuuki’s heritage and the details of his crimes. Tamaki, distressed by the conversation, cried out for Kikuhara to stop. The revelation overwhelmed Yuuki, causing him to lose consciousness. Midori intervened, halting the encounter and striking Kikuhara in anger.

Tamaki Anzai is regarded as a handsome man, bearing a strong resemblance to his son, Yuuki Anzai, with the notable distinction of having wavy, white hair, a trait influenced by his one-quarter English heritage. His light blue eyes are another feature passed down to Yuuki.

Due to his severe dependence on blood, Tamaki exists in a constant transformed state. His fingernails and toenails are elongated and claw-like, and his teeth protrude prominently from his mouth, impairing his speech to the point that he rarely speaks and, when he does, it is in short, quiet phrases. His eyes typically remain normal in color but can turn red under certain conditions.

Tamaki bears several self-inflicted scars caused by his claws, including visible marks on his cheeks, a scar on his left shoulder, and a large scar across his neck. He is commonly seen wearing nail protectors on his fingers and toes, along with handcuffs and a mouth-covering mask.

In his youth, Tamaki Anzai was described as wealthy, kind, charismatic, and magnanimous. Ambitious and hard-working, he harbored big dreams for the future and pursued them with dedication. His passion for architecture was evident both in and outside of class, often working alongside his then-girlfriend, Miho Kaneda. Deeply devoted to Miho, Tamaki’s life changed irrevocably after she was assaulted and later took her own life. Consumed by hatred, he sought revenge and killed her attackers without remorse.

Following the mass murders and his transfer to ONLO, Tamaki became withdrawn and despondent, closing himself off from others while endlessly mourning Miho’s death. Over time, however, his interactions with Midori Sako revealed a different side of him energetic, humorous, and even playful, as shown when he teased her about her bed hair. Through Midori’s influence, he gradually opened up, regaining much of his earlier warmth, protectiveness, and caring nature. Tamaki possesses keen intuition, which Midori has described as the ability to sense when there has been a death in someone’s family. He can also be shy and easily embarrassed, blushing when Midori came too close and even developing a fever at the thought of physical intimacy during the Hybrid Birth Project. Midori has remarked that he behaves “like a little girl” when it comes to romance.

While Tamaki no longer dwells on his past or regrets killing Miho’s assailants, he carries deep shame for the additional lives he took, regarding himself as nothing more than a murderer. He has expressed that revenge is never a true solution and has told Kirio Kikuhara as much. Tamaki believes he should have been executed rather than granted what he views as a relatively comfortable life at ONLO. He has struggled to understand why Midori would love him, fearing that he might harm or kill a human again.

Despite these doubts, his love for his family, Midori and Yuuki remains unconditional. His greatest wish is to be able to embrace them, though his physical condition prevents it. This longing brought him to tears when confiding in Midori. When he briefly encountered Yuuki as an adult for the first time, Tamaki was visibly overcome with emotion, even in that fleeting moment.

The given name Tamaki (環) means “ring,” “circle,” “link,” or “wheel.” His surname Anzai (安斎) combines an (安), meaning “peace” or “quiet,” with sai/zai (斎), which can mean “religious purification,” “Buddhist food,” “room,” “worship,” “avoid,” or “alike.”