The main character. A half-human, half-vampire who dislikes devils and believes that they should live separately from humans. He is a member of the Metro Police Department's Public Safety Division 5, a secret police force that specializes in devil-related crime. In his encounter with Tsukasa after an investigation, his bloodlust awakens. Despite his fear of hurting Tsukasa with his newly awakened devil half, he falls in love with her and forms a romantic relationship with her.
- Beauty Mark: Anzai has one placed on the left side of his upper lip.
- Childhood Friends: Anzai is friends with Yuuko Tamaru and Tadaya Hiruta, who were raised at the same ONL orphanage.
- Cool Mask: The gasmask that Anzai wore so that it could block the color and smell of blood.
- Covert Pervert: According to a character omake, he's "a perv at heart but isn't aware of it".
- A Date with Rosie Palms: Happens twice.
- Once, after he saves Tsukasa from Ochiai's sexual assault he escapes to a public washroom. There when he sees Tsukasa's blood on his hand, he gives in to his bloodlust and licks it off. He then proceeds to masturbate over tasting her blood.
- After Anzai and Tsukasa's first blood-training session, he steps out to "get some air". Cut to him undoing his belt and then ragged breathing underneath his inner monologue.
- Half-Human Hybrid: Anzai is a half-human and half-devil.
- Human Mom Nonhuman Dad: He was born to Midori Sako, a human researcher and Tamaki Anzai, a mass-murdering convict devil.
- Interspecies Romance: Him (half-human and half-devil) and Tsukasa (human).
- Raven Hair, Ivory Skin: Has dark hair and pale skin.
- Romantic Vampire Boy: He is the half-vampire Love Interest to Tsukasa.
- Sugar-and-Ice Personality: Anzai is seemingly distant towards Tsukasa at first. However, as time goes by, he ends up caring for her and tries his best to protect her from danger.
The heroine. A first-year graduate student at Keio University. She first meets Anzai after he arrests Akimura and eventually develops feelings for him. Later on, she receives a deep cut on her face after protecting Anzai from Zero Seven's attack.
The leader of Division 5's F Squad. He has great respect and compassion for his devil subordinates. He was once a member of the Investigation Department before being transferred to Public Security.
- A Father to His Men: He treats his devil subordinates with the same amount of respect and dignity as anyone else.
- Oblivious to Love: Jill and Shinjo are both romantically interested in him, and he has no idea that they're crushing on him... well, until he overhears the pair of them ranting to each other about how damn dense he is.
A half-American/half-Russian devil investigator who's a member of F Squad alongside Anzai. Also known by her nickname "Jill".
- Adaptational Badass: In the anime adaption she's an Action Girl who's able to take down devil criminals with a high physical prowess.
A hematologist who was dispatched to F Squad. He's in charge of giving physical examinations and providing sedatives to Anzai.
An officer from Investigation Division 1. He later temporarily joins Division 5's F Squad.
Megumi Ishimaru / Jason
An officer who belongs to Public Security Division 5's Squad A. He replaces Sawazaki as the new chief of Squad F under Kikuhara's recommendation. He's also a member of the CCC, going under the codename "Jason".
- Double Agent: In reality, his true identity is that of an investigator from Public Security General Affairs. His goal was to infiltrate the CCC to look for their members list.
- Exhausted Eye Bags: Unlike other devils who have heavy eye-bags due to not drinking blood from other humans, Ishimaru's eyes are just regular eye-bags from sleep deprivation after reading so many mangas and light novels at night without any rest.
- The Mole: The current leader of Squad F, he is revealed to be Jason from the Devil Extermination organization, the CCC. However, he is also a mole for the CCC, as his purpose in joining the organization is just to gather intel.
- Odd Friendship: Develops one with Asami.
- Otaku: He loves to stay up all night reading manga and light novels, which results in sleep deprivation and having heavy dark circles under his droopy eyes.
Johannes Kleeman / Hans Lee
A mysterious half-devil who first appears during Anzai's encounter with Zero Seven. He is able to drink blood without going through a full transformation.
- Big Eater: He eats like a horse.
- Bishōnen: Hans is a charming and handsome young fellow with long white hair.
- Cloud Cuckoo Lander: Hans is a little on the weird side.
- Half-Human Hybrid: Like Anzai, Hans is half-human and half-devil.
- Human Mom Nonhuman Dad: Inverted. Hans was born to a human father and devil mother.
- Peek-a-Bangs: His cover the left side of his face... for good reason.
- Red Baron: When he starts intervening to protect civilian devils from attacks by human vigilantes, he ends up with the nickname of "Silver Wolf".
- Technicolor Eyes: His devil left eye which he hides behind his Peek-a-Bangs.
- Tritagonist: The third most prominent character after the two leads.
A transgender devil bar-worker. Also goes by her alias "Oryo". Was framed for the murder of her co-worker.
Yuuki Anzai's father. A devil convict who'd murdered 15 people. Despite being sentenced to death he developed a severe blood addiction and thus was secretly transferred to the ONL for research purposes.
- Serial Killer: Tamaki is considered to be one of the most dangerous devils in history, as he killed more than 15 people when he lost control of himself.
A university student who was a friend of Tsukasa. He was arrested by Anzai for raping and murdering three women to redirect his bloodlust for Tsukasa.
Kaname Shirase / Zero One
A devil who serves as the Parliamentary Secretary of Health, Labor and Welfare. She leads and provides financial support to the CCC.
- Demoted to Extra: Her role in the anime adaption is severely reduced to a cameo appearance in Episode 8. She doesn't make any more appearances after and her identity as Zero One is never revealed.
Kirio Kikuhara / Zero Two
The commander of the CCC and the chief of Public Security Division 5's Squad A. A cruel and ruthless individual, he acts for his own purposes while following Zero One's instructions.
- Alliterative Name: Kirio Kikuhara.
- Big Bad: Kirio Kikuhara, who works for the police, is revealed to be the commander of a devil extermination organization.
- Dirty Cop: An officer who works for MPD. However, he is the ruthless leader of a devil extermination group.
- Lack of Empathy: He is a man who is unable to feel love towards someone either as a regular companion or being attracted sexually towards them. He also has no compunctions when throwing his companions away like a tissue to achieve his own goals.
- Obviously Evil: If you look at Kikuhara's face, especially his slanted eyes and devilish smile, then you notice something is not right about him.
- Parental Incest: His mother, Yuzuru, was an emotionally-absent parent for most of his life, leaving him in the hands of hired caretakers. When he hit age fifteen, however, she saw he'd grown up into a handsome young man and the dynamic changed. Horribly.
- Self-Made Orphan: He tossed his mother off a balcony to her death.
Kohei Nakamura / Zero Four
A TV Cameraman who's also a CCC combatant. During the Ikebukuro Incident he recorded the footage of the female newsreporter being attacked by a devil. Later on he tries to to kill Katagiri for being a witness to Fifteen's murder, but is stopped and arrested by Anzai and Hans. Afterwards he was detained but was shot dead when he tried to escape.
Naoya Ushio / Zero Five
A CCC spy who's a member of Public Safety Division 5's Squad C. He has a burn scar on his face.
- Good Scars, Evil Scars: Has a large, prominent burn scar on his left cheek.
- Well-Intentioned Extremist: He tells Tsukasa that he feels intense sympathy for devils because of the difficulties they face, having seen devil police officers struggling with exposure to blood at crime scenes. Thanks to his warped world-view, however, he seems to feel that the best way to help them is to kill them so they don't suffer those troubles any more.
Takeshi Makimura / Zero Six
A CCC sniper who's a member of the Public Security Division 5's Squad B.
- Asexual: Heavily implied to be this. He develops romantic feelings for Mayu, but he doesn't feel any sexual urges or desires towards her.
- Double Agent: Like Ishimaru he is also an investigator from Public Security General Affairs who was sent to infiltrate the CCC.
Nanako Tenjo / Zero Seven
A sniper with the CCC. She holds a strong hatred for devils and has killed many of them. However, Tsukasa's relationship with Anzai makes Nanako start to reevaluate her views on devils.
- Boom, Headshot!: Her preferred method of assassination.
- Cold Sniper: She works at range, a sensible approach when dealing with fast, strong demons.
- Freudian Excuse: Nanako becomes the elite sniper of the CCC organization because her mom was raped and killed by a devil and then she was persuaded by Kikuhara to join his side to exterminate all the devils.
Ken'ichi Yoshii / Zero Nine
A youth who is a member of the CCC. He specializes in machine engineering and computer hacking. He has a one-sided crush on Nanako and leaves the organization with her to protect her from being eliminated.
- The Smart Guy: The group's computer expert.
Mayu Sumimori / Eleven
A woman in charge of intelligence gathering and accounting for the CCC. She has an inferiority complex regarding her appearance.
Akihito Kanzaki / Queen
A non-binary doctor who works for the CCC. He leads a mercenary group composed of ReMI devils.
- Adapted Out: He doesn't make an appearance in the anime adaption. The only mention he gets is a scene with a whiteboard containing a listing of the CCC members' codenames.
Ren Murakami / Fifteen
A part-time worker who's one of the CCC's combatants. He stabs a female newsreporter during a live tv broadcast to carry out his organization's "Plan B". After fulfilling his role, he is killed by Kikuhara to remove evidence of the incident.
Yuuki Anzai's biological mother and wife to Tamaki Anzai. She is the director of ONL's Bionomic Research Department and a member of the R2PC.
- Amazingly Embarrassing Parents: While talking to Tsukasa about the mechanics of managing human/devil sex, she cheerfully describes her sexual experience with Anzai's dad, using a written detailed plan. She does use clinical terms for most of it, but Tsukasa spends a lot of time blushing herself half to death. After all, this is Anzai's mother, taking Too Much Information to breathtaking heights.
- Second Love: Is this to Tamaki as years before he met her he dated a human woman named Miho Kaneda.
A psychosomatic internist for devils and a member of the R2PC. He seems to be quite familiar with Anzai and Hans.
The owner of Bar Sakaki, a liquor store that also acts as a base for F Squad. He's also a rental manager and owns the room that Anzai lives in.
- The Bartender: He runs a bar where F Squad mostly spends their time.
Tsukasa's best friend. She aims to become a reporter. She starts to worry for Tsukasa's well-being when she hears that she's in love with a devil.
A Chinese doctor who works at Shirase Hospital. She's one of Hans' blood donors.
A professor at Keio university. He attempts to sexually assault Tsukasa but is stopped by Anzai and ends up being brutally beaten. After the incident he gets fired from his job.
- Laser-Guided Karma: After Ochiai tries to rape Tsukasa, he gets beaten by a transformed Anzai, gets fired from his position, his wife divorces him and lastly, one of the students leaks his personal information, which ruins his reputation.
- Rape Is a Special Kind of Evil: Needless to say, many people didn't like what Ochiai has done after he tries to rape Tsukasa by force.