Mei Kihara is the protagonist of "My Dear Cold Blooded King." She is currently training in the Blood Core and was formally an assistant court physician in the Blood King's palace. She is also the temporary cover fiancée for the Blood King.

• Action Girl: Although she isn't a professional fighter, Mei is trained in martial arts, and is also receiving official training to improve her skills.
• Aloof Dark-Haired Girl: She’s more on the quiet side, but is friendly. However, she gives this impression because of her reserved nature.
• Badass in Distress: Because she’s still a Badass Normal, she isn’t able to fend off Kozuke’s men.
• Badass Normal: She's very good at martial arts and can more than hold her own...except when faced with professionally trained soldiers and assassins.
• Break the Cutie: What Kozuke’s abduction of her (and painting on her) did. She isn’t as broken as many examples, but most characters note a distinct change in her personality.
• Character Development: Becomes less impulsive and more emotionally sensitive as the series goes on, especially after the former quality gets her into trouble one too many times with the palace's authority figures.
• Cool Sword: Initially, the only weapon she is capable of using is a kodachi. Given that this is not enough to ward off more skilled threats, however, she is later taught to use a naginata under Katsu.
• Damsel out of Distress: One of her first appearances is when she finds an injured boy in the woods, and seeing that he is about to be attacked, defends him against his would be attackers.
• Deadpan Snarker: Boy, is she. Definitely one of her major personality traits.
• Dude Magnet: Katsu likes her, Ryusaki likes her though it is uncertain as to if these feelings are romantic or platonic, the ambassador likes her, Hayashi is practically lusting for her, and Kozuke, also known as Yuuta, has liked her since they were children. Wow, Mei.
• Feminine Women Can Cook: Mei is noted as being quite the good cook.
• Honey Trap: Was an unwitting one in Ryusaki's broader plan to capture Kozuke. That is, before the former learns that the latter was targeting her all along.
• Lady of War: Not quite yet, but she’s in training to become one.
• Luminescent Blush: She gets flustered and embarrassed easily.
• Naginatas Are Feminine: Her eventual weapon.
• Unskilled, but Strong: There is no doubt that she is a great fighter, but compared to the highly trained other characters, is out of her depth.
• She Cleans Up Nicely: She’s noted to be already beautiful naturally, but when she gets dressed up…
• So Beautiful, It's a Curse: She happens to attract a lot of unwanted attention.
• Tomboy with a Girly Streak: She’s tough and a good fighter, but doesn’t have a disdain for more feminine activities, such as cooking and seems to enjoy some of them.

One of the first people Mei meets upon moving into the palace. Despite a hostile first encounter between him and Mei, the two are quick to take an interest in each other, despite the latter's suspicions. Their relationship is further complicated when it's revealed that he is Katsu Asukai, the current Blood King.

• Action Politician: The ruling Blood King and no slouch when it comes to swordsmanship, especially given how many people he's seen cutting down.
• Berserk Button: While he is generally more kind and well-intentioned, he is quick to irrationality and anger when the people he cares for are placed in harm's way.
• Beneath the Mask: Generally appears cold and distant, mostly to maintain his image as the Blood King, but is actually very warm, emotional, and compassionate.
• Good Is Not Soft: He is shown as being very gentle and caring towards those he loves, but put them in harm's way and he will not hesitate to draw his sword.
• Just Trying to Help: Katsu ended up doing the complete opposite of this to both Yuuta Murakami and Shibisaki, his well-meant intentions only hurting them instead. He is also noted to branch often into Condescending Compassion, fuelling anger on Kozuke's part.
• Love Epiphany: Has one for Akane when he realizes the qualities he though he loved in Mei were actually the qualities he loved in her.
• Luminescent Blush: Becomes more and more prone to this as the series goes on, especially when Mei is involved.
• Mr. Fanservice: Gets more than his fair share of topless scenes, and even when he's fully dressed, a substantial number of his outfits show off his bare chest.
• Mystical White Hair: Mei almost mistakes him for a ghost because of this.
• Red Oni, Blue Oni: Zig-zagged. On the surface, he appears to be the stoic blue to Hayate's hedonistic red. When the two are alone, however, then they switch, as their true colours primarily show then.
• Reluctant Ruler: Is more than willing to wash his hands of the legacy and being 'the Blood King.'
• Warrior Prince: Well, he was. Even now as the King, he's still got the 'blood' bit down.

The lieutenant of the Blood Core and the Blood King's decoy. While he initially appears to be nothing more than an obnoxious flirt, he is later revealed to be the bastard of the previous Blood King, thus making him a prince and Katsu and Osamu's older half-brother.

• Anti-Hero: Wants the best for the kingdom and the Kihara family. Not that this prevents him from using Mei as an Unwitting Pawn in his pursuit of Kozuke.
• Beneath the Mask: Appears as a hopeless flirt on the surface, but is actually very pragmatic and remorseless, arguably more so than his half-brother, the acting Blood King.
• Belligerent Sexual Tension: Goodness gracious, can he and Mei have a conversation without bickering and teasing?
• Chivalrous Pervert: Despite being very flirty, persistently so, he is a genuinely good person, although more on the Anti-Hero spectrum.
• Heroic Bastard: Is the eldest son to the previous Blood King and a concubine. That being said, this doesn't stop him from trying to exert his authority to work towards what he sees as the greater good.
• I Will Protect Her: Promises Daisuke in Episode 64 that if anything were to happen to him he would protect Mei.
• King Incognito: To the point where he pretends to be just a high ranking officer in the his army and a mere decoy to Katsu to hide the fact that he's the real Blood King.
• Plucky Comic Relief: Appears this way at first. Later subverted when it's revealed how cold and serious he really is.
• Red Oni, Blue Oni: Zig-zagged. On the surface, he appears to be the hedonistic red to Katsu's stoic blue. When the two are alone, however, thus allowing for their true colors to come out, they switch.
• Royal Blood And as it turns out, is the only real son of King Ozuru.
• Unrelated Brothers: With Daisuke Kihara.

Kôzuke is the leader of the Hebi Gang. He rose to power roughly six years ago and is referred to as "Master," by his underlings. He was once childhood friends with Katsu and Shibisaki as well as Mei's childhood sweetheart. Now, he wishes to overthrow the Blood king and take Mei as his own.

• Benevolent Boss: He seems to genuinely care for his subjects and, so long as they are loyal and obedient, treats them very well, judging by how his people fervently refer to him as the "True King," and seem to be quite content living under him, believing that he will be the one to usher in a new age of peace.
• Childhood Marriage Promise: In a flashback scene in Episode 57, Kôzuke promises to marry Mei once they're older, and make her his "princess." He later upgrades this vow to "Queen."
• Defiant Captive: Played with. While he has tried to escape the palace at least once, during which he meets Mei for the first time, he eventually feigned compliance in order to bide his time.
• Driven to Villainy: Though he admits he became drunk on the power he gained, his rise to power and rebellion had roots in his traumatic past, having scars both inside and out from the successive Blood kings.
• Evil Former Friend: Is this to Katsu and Shibisaki.
• Evil Redhead: Redhead? Check. Evil? Check...?
• Is That What He Told You?: He can either play around with this or be more genuine in "correcting her misgivings." He reveals that Daisuke was mostly responsible in him having to break his promise to her and that what she thinks is the truth isn't always.
• Kick The Son Of A Bitch: Kills Hayashi after he boasts to Kozuke his plans to either kill Mei or force her to submit to him as his concubine.
• Mind Game Ship: Towards Mei, he is soft-spoken, polite, flirty and completely manipulative, causing Mei a good deal of trauma.
• Really Royalty Reveal: Not much of a surprise, since it was hinted at more than once before with all the "true King," business but it was said out flat in Episode 094.
• Ruling Family Massacre: Hinted at what occurred when King Ozuru conquered Ashiroi, Kozuke's kingdom. This caused him both physical and mental scars.
• Terms of Endangerment: Wants to make Mei his queen when he deposes the current king, and subsequently refers to her as “my love.” This is all in spite of the fact that Mei has moved on from him and that he has no regard for her consent (He drugs her, marks her with tattoos, dresses her in revealing outfits, and forcibly embraces and kisses her). He even goes so far as to threaten Mei’s younger brother if she shows anyone the first set of tattoos he gives her.
• Villainous Crush: He was in love with Mei before he went down the villain route and still is now.
• We Can Rule Together: That and marriage are his two main points in keeping Mei by his side.
• Yandere: Kozuke is notably obsessive when it comes to Mei to the point of being a borderline Yandere. He demonstrates such qualities as "marking" her, threatening her to stay away from other men and showing his own control over her. Additionally, he "baits" her with information he knows she wants more than anything and keeps look-alikes of Mei as concubines.

Shiori, otherwise known as Sumire, was a prostitute with whom Ryusaki had a former romantic relationship with. She is currently Kozuke's right-hand.

• My Master, Right or Wrong:
• Replacement Goldfish: Although she went into the relationship with Kôzuke knowing that she was only a replacement for Mei, (it helped that she looked very much alike her) she came to fall for her "master," though he still only has eyes for the "original."
• Samus Is a Girl: Is initially believed by both the characters and the audience to be a man.

General Shibisaki is the second highest in command of the entire army, directly after Katsu as well as being a member of the Core.

• The Stoic: Probably the least friendly of the cast. He rarely shows any emotion past disgust and only calls people by their title or last name. However, he has shown remorse over Daisuke.
• Good All Along: Though he initially seemed to be suspicious due to his treatment of Mei and alliance to Kozuke, he had secretly been working with his own faction to stop the conflict between the Hebi Gang and the kingdom.

Mr. Fujioka is the court physician and Mei's former mentor. He is good friends with Sanjiro and Aiko Kihara.

• Like a Son to Me: Thinks of both, Sanjirou Kihara (Mei's father) as this alongside Kozuke, also known as Yuuta Murakami.
• Luke, I Am Your Father: Reveals to Katsu that he is his real father, much to Katsu's delight.

Osamu Asukai is a Prince and the younger brother of Katsu Asukai and Hayate Ryusaki.

• Chuck Cunningham Syndrome: After his kidnapping that sets off the plot, he is (almost) never seen again. Lifelight has admitted to flat-out forgetting about him.

Daisuke Kihara is Mei's elder brother. He is said to have died before the start of the series in the last great war with the rebellion, sacrificing himself for his men while staging a counter-attack against the enemy.

He was a former lieutenant general and quite the decorated officer. He was given the promotion to general in a posthumous ceremony.

It is later revealed he is actually still alive, and has secretly been assisting Shibisaki's plans for peace after killing everyone else in Shibisaki's group in the belief he was a traitor helping Kozuke.

• Beware the Nice Ones: While he was shown to be normally light-hearted and cheerful as well as a kind brother and mentor, it is easily forgotten he was a high-ranking member of the Blood Core, which is a group of the military's most elite and bloodthirsty soldiers.
• Big Brother Instinct: Daisuke was somewhat protective of Mei, not wanting to her be involved or even know about his being in the Blood Core. His protective side also shows in a flashback when Ryusaki sees his sister for the first time, as he catches the lieutenant staring at Mei and warns him who he’s “ogling”.
• Big Brother Mentor: Not only to Mei, whom he taught to use a Kodachi, but to Ryusaki as well.
• Faking the Dead Turns out he's been alive all along, just pretending to be dead to help Shibisaki's goals without interference.
• Heroic Sacrifice: Died in battle so that his men could survive...or so the lie went. He really died trying to bring down Kozuke, whom he feared, given his obsession with Mei, would try to go after his little sister. Still a heroic death, though.
  • Or it would have been, had it not turned out he isn't actually dead at all.

Prince Hayashi is the elder brother of Princess Akane and an old friend of Ryusaki. He is very much so against Mei's "engagement" to the Blood King and has no qualms with doing something about it.

• Asshole Victim: Given his blatant classism and revelation that he frequently rapes women including his own sister,nobody felt sorry for him when he was beaten almost to death by Katsu and then was actually killed by Kozuke
• Brother–Sister Incest: Revealed to have frequently raped his sister Akane.
• Oh, Crap!! Gets his first one when he monologues to Ryusaki about how he wants to break Mei's will and maker her his concubine, only for Ryusaki to reveal Mei is his bride. This leads directly to his second when Ryusaki reveals that HE'S actually the true King, and that Katsu doesn't have any royal blood, making his plans to get Katsu to marry his sister fall to ruin. The last is when he AGAIN blabs about trying to rape Mei and his desire to either kill her or make her his concubine, only to Kozuke, who he had thought his ally in taking down the Blood King. Kozuke then reveals his plan to marry Mei and make her his queen, leaving Hayashi to have a brief Oh Crap moment right before Kozuke kills him.
• The Evil Prince: Shaping up to be more of a villain than Kozuke himself.
• Hate Sink: Other than his looks, Hayashi doesn't have a single redeeming quality. This is even lampshaded in a humorous behind the scenes chapter, in which Kozuke reveals that, while he himself gets comments from fans about how hot he is and how much they love him, all the comments shown for Hayashi are about how much the fandom hates him. And this was BEFORE he was revealed to be a rapist.
• Oh, Crap!! Gets his first one when he monologues to Ryusaki about how he wants to break Mei's will and maker her his concubine, only for Ryusaki to reveal Mei is his bride. This leads directly to his second when Ryusaki reveals that HE'S actually the true King, and that Katsu doesn't have any royal blood, making his plans to get Katsu to marry his sister fall to ruin. The last is when he AGAIN blabs about trying to rape Mei and his desire to either kill her or make her his concubine, only to Kozuke, who he had thought his ally in taking down the Blood King. Kozuke then reveals his plan to marry Mei and make her his queen, leaving Hayashi to have a brief Oh Crap moment right before Kozuke kills him.
• Serial Rapist: And seemingly proud of it too.
• Sibling Yin-Yang: Is as hateful and despicable as his sister Akane is kind and caring.
• Smug Snake

The younger sister of Hayashi, Princess Akane is a sweet girl who used to be engaged to Katsu.

• Hair of Gold, Heart of Gold: Has golden hair and is one of the nicest people in the series, as opposed to her mean brother Hayashi, who also has golden hair.
• Hidden Depths: Despite initially seeming to be a meek pawn of her brother, she hates him for his cruelty to others and because he repeatedly raped her.
• I Want My Beloved to Be Happy: Despite her feelings for Katsu, she genuinely thinks Mei is the best person for him. Fortunately for Akane, Katsu seems to have realized that it was actually her he's loved all along.
• Nice Girl: One of the nicest people in the series.
• Sibling Yin-Yang: Is as nice and caring as her brother Hayashi is hateful and cruel.
• Shrinking Violet: Doesn't speak up for herself much at first, due to her overbearing brother controlling her life.
• Took a Level in Badass: She didn't become an outright Action Girl like Mei, but she goes from being a meek Extreme Doormat to her brother to willingly joining a dangerous mission to capture Kozuke by pretending to be Mei.

• Forbidden Love: Thinks this is what he shares with Mei after he finds out she's engaged to the King. Mei doesn't see it this way.
• I Want My Beloved to Be Happy: Insists that Mei forget about her feelings for him due to being engaged to the King, despite Mei not actually being in love with him.
• Large Ham: When around Mei.