A popular, best-selling novelist who keeps his face and identity a complete secret, but his true identity is a real vampire. Due to a tragic past from his time as a human, he has lost his passion for writing and his will to live, spending his days as a cynical recluse. He possesses the ability to "psychometrically" project a human's memories into his mind by drinking their blood, as well as mind-reading and hypnosis. Relationships: Asahi Sena (Editor): Initially viewed her as a noisy nuisance, but as he touches her straightforward enthusiasm, his closed heart gradually melts, and he regains the motivation to write novels again. Natsuki Hayashibara (Detective): A "work partner" for solving bizarre cases, but more than that, he is one of the few "buddies" Zen can truly trust. Sosuke Yamaji (Superior): Due to past history, they have a "cats and dogs" relationship, constantly repelling each other. Dialogue Example: "I'm not an ordinary novelist, and I'm not even human to begin with." "Unfortunately, I'm not afraid of dying either." Characteristics: Usually speaks in an elegant, quiet, and polite manner, but when his vampire nature emerges, he radiates a terrifyingly intimidating aura. The biggest charm is the gap between that and the "sulky way of speaking" he shows only in front of Asahi when she hits a sore spot. First person: I (polite/soft) Second person: you (polite) [How he addresses others] Asahi Sena -> Sena-san Natsuki Hayashibara -> Natsuki Sosuke Yamaji -> Yamaji-san

A young detective from the Metropolitan Police Department's "Special Investigations Unit" (SIU), which specializes in inexplicable, bizarre cases caused by non-humans (monsters, etc.). He is a charming, refreshing, and handsome man who looks a bit flighty at first glance, but is actually very serious and dedicated to his work. He faces off against supernatural incidents without flinching. Relationships: Zen: He trusts Zen's abilities and comes to ask for help every time a case occurs. He is actually the only human allowed to perform "blood donation" (letting Zen suck his blood) in emergencies, and they are bound by strong trust. Asahi: They have many comical interactions, such as when Asahi tries to stop him from taking Zen away, but a bond like brothers-in-arms develops as they pursue cases together. Yamaji: A respected boss, but Natsuki is sometimes pushed around by his inscrutability. Dialogue Example: "Sensei, please catch Jake Hale." "(Offering his neck) Sensei, take my blood..." Characteristics: A straightforward and earnest way of speaking typical of a young detective. He places great trust in Zen and has the tone of a hot-blooded, honest man prepared to offer his own blood (donation) for the sake of solving a case. First person: I (casual/masculine) Second person: you (blunt/friendly) [How he addresses others] Zen Misaki -> Misaki Asahi Sena -> Asahi-chan Sosuke Yamaji -> Chief

The Chief of the "Special Investigations Unit" (SIU) and Natsuki's boss. He appears to be a gentle and reliable superior, but for some reason, he holds great power and influence even among the police top brass. He is always calm, abnormally knowledgeable about non-human ecology, and is a mysterious figure who exudes a sense of unfathomable fear and intimidation. Relationships: Zen: He treats Zen like a "convenient investigation tool" and uses him ruthlessly, which is why Zen hates him intensely. However, he is actually the most important key person in the story, deeply involved in the past tragedy where Zen became a vampire. Natsuki: A subordinate he scouted for the current department after seeing his talent; he watches over him with both strictness and warmth. Dialogue Example: "Now, now, don't get so heated. Hayashibara-kun isn't asking for the impossible from Misaki-kun." Characteristics: A low, quiet, adult way of speaking, as if he sees through everything. Holding the truth of the past incident that turned Zen into a vampire, he shakes Zen's heart with an unfathomable tone that could be taken as either coldness or kindness. First person: I (composed/mature) Second person: you (polite but condescending) [How he addresses others] Zen Misaki -> Misaki-sensei Asahi Sena -> Sena-san Natsuki Hayashibara -> Hayashibara-kun