A top student of Assault Side, who, for some reason, demoted himself to the more rear-line Inquest Side. When sexually aroused, he enters a state called "Hysteria Savant Syndrome" (HSS), also known as "Hysteria Mode".
- Accidental Pervert: He gets himself in all sorts of embarrassing incidents with girls, including groping them or seeing them underdressed. Considering how his power works, this can be a problem or save his life.
- The Ace: In HSS mode, he's a Genius Lightning Bruiser and a smooth-talker to boot.
- Almighty Janitor: Especially in HSS, though it's hinted that normally he's stronger than his "E rank" would indicate.
- Anchored Ship: It's heavily implied both in the light novels and the manga that Kinji refuses to act on his feelings for Aria because he's convinced they're going to be separated sooner or later thanks to their different stations in life.
- Badass Normal: He aced the Butei entrance exam and is shown to be highly competent even without HSS.
- Bullet Time: One of his powers under HSS.
- Butt-Monkey: His girls love to make his life difficult for him and his flat.
- Chick Magnet: About every girl he knows is in love with him.
- Chivalrous Pervert: While in HSS, he becomes a very smug and smooth-talking ladykiller, and feels compelled to protect any girl in front of him no matter what. This peeves Kinji to no end.
- Clueless Chick Magnet: He has many female admirers. He either doesn't notice or chooses to ignore the signs. Subverted because then novels make it clear he DOES know.
- Crazy-Prepared: After defeating Sherlock Holmes, Kinji also starts carrying with him his father's triple-burst IMI Desert Eagle, as well as a seax inherited from Sherlock.
- Cursed with Awesome: HSS grants him superhuman abilities, but it is only activated by sexual arousal, and under such a state Kinji turns into a suave ladykiller, which he thinks is detrimental to his academic life.
- Deadpan Snarker: Tends to respond this way to his comrades' quirky behavior.
- Deus Sex Machina: He needs to be sexually aroused (usually by experiencing Marshmallow Hell or kissing) to activate his HSS.
- Dual Wielding: Latest light novel volumes promote him into the "third Quadra", after Aria and Riko.
- The Dulcinea Effect: Kinji inherited this genetically. It's a side effect of his Hysteria mode. He can't not help a girl in trouble.
- Famous Ancestor: Though not explicitly mentioned, he is obviously implied to be a descendant of Kagemoto Tohyama (popularly known as Kinshiro or Kin-san), a real life chief of police from the Edo period who became a folk character in Japan.
- First Kiss: With Aria, which also doubles as a deliberate HSS activation to him.
- First-Person Smartass: Snarks a lot in his head.
- Humiliation Conga: He was forced to mull leaving Butei after he and his (supposedly-dead) older brother Kinichi was subjected to this after the latter's rescue attempt aboard a sinking ship, but with the shipping company unwilling to take responsibility and instead scapegoating him.
- I Just Want to Be Normal: After his brother Kin-ichi's supposed death, he just wants to be done in Butei life and plans to tranfer to a normal high school as soon as the year finishes. The problem is, his special ability and relationship with Aria (amongst other things) make that a lot more difficult than he would like. In volume 7/chapter 87, Koko outright tells him that because of his gift he'll never be able to live among "normal" people.
- It Is Pronounced Tro Pay: His surname isn't said as "Two-yama". It's "Toh-yama".
- Knife Nut: He is pretty skilled with his butterfly knife, even without entering HSS.
- Mistaken for Pedophile: By his classmates as one due to his closeness to the diminutive Aria. She is the most effective catalyst for his HSS. For example, in Episode 10, he managed to resist arousal from Riko in just her lingerie, but couldn't hold on any longer once he saw Aria taking off her socks.
- Mistress and Servant Boy: Aria keeps asserting that Kinji is her slave.
- Oblivious to Love: Averted. The light novels make it especially clear that Kinji is fully aware of other girls' romantic interest in him, but just chooses to play dumb rather than face it. There's an especially strong case in Kinji's own feelings for Aria. He knows perfectly well how he feels about her, he just refuses to acknowledge it, even in the privacy of his own head.
- Overshadowed by Awesome: Ironically, by his own HSS-addled alter-ego. He knows it and hates that fact.
- Spell My Name with an "S": His surname via the "toh" part can sometimes be written as either "Toh" or "Too", though the latter is more accurate due to the official furigana having an extended "o" vowel instead of he usual extra "u".
- Straight Man: Usually plays this role when surrounded by Aria, Riko and/or Shirayuki − and later Reki when she turns out to be Not So Above It All. He can't do much when two of those four get into a fight though.
- Super Mode: His Hysteria Mode. He also has the "Berserk HSS" upgrade, which is triggered by jealousy.
- Super Reflexes: One of his Hysteria mode's powers.
- Tall, Dark, and Snarky: He's very bitter, cynical, and sarcastic, yet good-looking young man.
- Tsundere: Type A. He usually treats Aria with indifference, but there are times when he is kind to her.
- Tsurime Eyes: Has a sharp eye shape and a sharp tongue to match.
- Unwanted Harem: He has Aria, Shirayuki, Riko, and Reki after him. And that's just the top of the iceberg.
- Wacky Marriage Proposal: Played with in volume 7/chapter 93. He offers Aria a ring for her birthday, but doesn't know on which finger he should put it It turns out it fits just right on her left ring finger. Aria gets the "message", panicks and then prompty faints in front of a clueless Kinji.
- Weapon of Choice: A Beretta 92FS Inox modified to fire a three-round burst, which he conveniently names "Beretta Kinji Model", as well as a butterfly knife. Later gets a seax knife given to him by Sherlock Holmes.
Aria Holmes Kanzaki
A diminutive top student of Butei High's prestigious Assault Side. Looking for a fitting partner, her attention falls on Kinji, whom she quickly declares her "slave". She is also the great-granddaughter of the most powerful and intelligent detective in history, Sherlock Holmes.
- A-Cup Angst: She hates to be reminded of her small breasts. It doesn't help all her love rivals have a bigger bust size than her.
- Animal Motifs: Cats. She is fond of "Leopon" stuffed cats, some key scenes involving her have random purrs, and in Episode 2 she even growls like a cat. In Episode 6 Shirayuki even calls her a "thieving cat"note for freeloading with Kinji.
- Badass Adorable: She may be small and adorable, but she's also part of Butei High's Assault Side so she can and will kick your ass.
- Betty and Veronica: The aggressive, exotic Veronica to Shirayuki's sweet, longtime friend Betty.
- But Not Too Foreign: Her mother is Japanese and her father is half English, half Japanese.
- Catchphrase:Japanese: "I'll blow a hole through you!"
English: "I'll pump you full of holes!"
- Child Prodigy: From a young age, she showed great talent in being a Butei. It's a result of her being a descendant of Sherlock Holmes.
- Clear Their Name: Aria's primary motivation for attending Butei High is to help clear her mother, Kanae, of charges of being the "Butei Killer", which automatically sent her to 862 years in prison. If successful, Aria could shave off centuries of prison time for her, and at the best-case scenario, even clear her altogether.
- Clingy Jealous Girl: She gets very jealous whenever Kinji gets too close to another girl.
- Curtains Match the Window: Aria's eyes and hair are reddish-pink.
- Cute Little Fangs: She's drawn with sharp fangs to complement her feline tendencies.
- Double Standard: Abuse, Female on Male: She tends to hit (or even shoot at) Kinji on a regular basis, for the flimsiest reasons. She gets somewhat better as the series goes on, if only because of her growing feelings for him.
- Dual Wielding: A pair of M1911s and a pair of kodachis. She's thus one of the "Quadra".
- Early Installment Weirdness: Her first appearance has her wearing sneakers along with her uniform, almost in a sukeban-like manner, instead of the proper dress shoes she wears since. She also wore initially a hairpin to keep her bangs up, but she drops it to cover the forehead scar she receives in one of the first cases.
- Famous Ancestor: She's the fourth-generation descendant of the titular Sherlock Holmes, explaining the "H" in her name.
- Fear of Thunder: She's quite afraid of thunder. This presents problems in missions where it's raining.
- Fiery Redhead: She has quite the Hair-Trigger Temper and gets passionate very easily during her missions.
- First Kiss: With Kinji, which also doubles as a "Shut Up" Kiss to her in order to pacify her after she was revived after being critically hit in the chest by Riko.
- Forehead of Doom: She has a rather big forehead, something she's proud of and Kinji tends to tease her about.
- Girlish Pigtails: She ties her hair into twintails; another trait that identifies her as a Tsundere.
- Guns Akimbo: According to IMFDB, her weapons are a pair of customized Colt Model Governments, which is a civilian variant of the of the military issued Colt 1911A1 used in World War II.
- Hair-Trigger Temper: Being a Fiery Redhead, she gets extremely angry with minimal provocation.
- Horned Humanoid: Her red hair pins evoke this, giving her an aptly devilish appearance.
- Idiot Hair: Not a very noticeable, but she has one hair that sticks out from her bangs.
- Insufferable Genius: Somehow is A LOT like Holmes himself via the insufferable-part, which is quite clear in the beginning where Kinji shows clear annoyance living with her (making their dynamic akin to how Watson had to start out with Holmes), and her assumptions of the source of Kinji's HSS being off the mark for most of the series.
- Lamarck Was Right: Averted. Supposedly, Aria is a deficient version of her great-grandfather, unable to solve cases with the Holmes deductive skills.
- Lethal Chef: Cooking is the only thing she's no good for.
- Little Miss Badass: Despite her small size, she can easily kick your ass.
- Locked into Strangeness: The 'Scarlet Bullet' changed her blond hair and blue eyes into the reddish-pink she has now.
- Luminescent Blush: Very prone to blushing around Kinji, especially when he's in his Hysteria mode.
- The Napoleon: As typical with the Shana Clones, Aria's temper is as short as her stature.
- Miss Conception: She thinks kissing instantly leads to pregnancy.
- Mistress and Servant Boy: Keeps asserting that Kinji is her slave.
- Multi-Ethnic Name: An Italian given name, an English middle name and a Japanese surname.
- The Musketeer: She fights with both guns and katanas.
- Mysterious Middle Initial: Turns out the H. stands for "Holmes", as in Sherlock Holmes.
- New Transfer Student: She enters Butei High School as a transfer student at Kinji's class.
- Ojou: She claims to be an "aristocrat" and certainly acts haughty.
- Older Than She Looks: She's a second-year high school student like Kinji, but her short height and underdeveloped body make her look like a preteen. Her stunted growth is due to the 'Scarlet Bullet' embedded in her back.
- Omniglot: She knows seventeen languages.
- Pretty Freeloader: She settles in Kinji's apartment without asking for his permission and gets to stay there without ever having to pay or help in the house chores.
- Rapunzel Hair: Her Girlish Pigtails reach way below her knees. She's an aristocrat, after all.
- Red Eyes, Take Warning: She has big red eyes and you better watch out when you're near her, she's quick to fire her guns at you.
- Scars Are Forever: After a brush with death during the bus bomb incident, she has since kept a small X-shaped scar on her forehead (now hidden by her hair) as a reminder.
- Shana Clone: Older Than She Looks small, flat-chested teenage girl, reddish Rapunzel Hair tied into Girlish Pigtails, Grade S Zettai Ryouiki, aggressive Tsundere, refers to her Love Interest as her slave, has the same affection for peach buns that the original had for melon bread and voiced by Rie Kugimiya to boot. She's possibly the 5th Tsundere Wonder.
- Super Drowning Skills: She's unable to swim.
- The Three Faces of Eve: The Child (diminutive and temperamental, with bouts of innocence).
- Tiny Tyrannical Girl: She is only 142 cm or a little under 4'8". Her first request to Kinji is to become her slave. She later orders the same thing to Shirayuki, and sometimes talks about how she has to "train" them. Don't try to disobey, or she'll make you full of airholes.
- Token Mini-Moe: The only member of the cast to look like a child.
- Trademark Favorite Food: Peach buns.
- Trigger Happy: She is quick to use her guns when she gets angry.
- Trouser Space: She hides a pair of guns under her skirt.
- Tsundere: Harsh Type; haughty, abrasive, demanding and occasionally affectionate. Kinji notes that she smells 'sweet and sour'.
- Tsurime Eyes: As expected from a haughty Tsundere, she has a sharp eye shape.
- You Gotta Have Blue Hair: Her hair is bright reddish pink. It is not natural but an effect of the "Scarlet Bullet", thus subverting this trope. She's actually blonde.
- Zettai Ryouiki: Rank S. She wears black thigh-high stockings, has Girlish Pigtails and is a Tsundere.
Kinji's childhood friend and a Miko of the Hotogi Shrine in Aomori Prefecture.
- Alliterative Name: Himiko Hotogi.
- Betty and Veronica: The sweet, longtime friend Betty to Aria's aggressive, exotic Veronica.
- Beware the Nice Ones: Kind, affectionate, bashful, and when she heard that Shinji was threatened by a serial killer copycat, she started talking about lopping limbs off.
- Bitch in Sheep's Clothing: Most of the time, she's sweet, gentle and delicate. Until she switches to Yandere mode.
- Childhood Friend Romance: Her ultimate goal with Kinji to move from "girl he befriended as a child" to "beloved wife".
- Clingy Jealous Girl: Do not be within a 2 meter radius from Kinji in her presence.
- Club President: She's president of various clubs including the gardening club, handicraft club, and girls' volleyball club.
- Dull Eyes of Unhappiness: Whenever she's slipping into Yandere mode, especially towards Aria, her eyes go blank.
- Famous Ancestor: Himiko, legendary shaman queen of Yamataikoku, who ruled some 2000 years ago.
- First Kiss: With Kinji, though technically this is already the guy's second (the first being Aria, of course).
- Friendless Background: Implied — as a child she was not allowed to go outside, and was severely punished for going out with Kinji. She was also only able to attend Butei High due to her clan's approval.
- Healing Hands: As a priestess and a Stealth, she can use healing magic to a limited degree.
- Hime Cut: Fitting with her status as a Yamato Nadeshiko and the descendant of a legendary Japanese shaman queen, she wears her hair in this style: long in the back, even bangs and sidelocks.
- Katanas Are Just Better: Her katana, called "Irokane Ayame", forged from the Unobtanium of the same name.
- Meaningful Name: Shirayuki means "white snow". But Riko delightfully points out that she wears black underwear.
- Miko: Her family is a hugely influential clan of Shinto priests, and she's no exception.
- Multi-Melee Master: Weapons include a katana and a kusarigama, among others.
- Only Known by Their Nickname: "Shirayuki" is an alias to conceal her real name, Himiko.
- Patient Childhood Love Interest: She's been in love with Kinji since they were kids and can get extremely (and weirdly) demonstrative of it. Her "patience" tends to run out quite frequently, but Kinji is rather creeped out, as she looks and sounds positively insane in those moments.
- Playing with Fire: Her offensive magic is based on this, with Irokane Ayame acting as a Flaming Sword.
- Rapunzel Hair: Smooth, black hair that elegantly falls to her waist, lending to her noble appearance.
- Student Council President: She's the current student council chairman.
- Tareme Eyes: Being a shy, polite and demure girl (most of the time) she has the rounded eyes shape.
- The Three Faces of Eve: The Wife (a mild-mannered, albeit potentially violent Yamato Nadeshiko, who has considerable domestic skills, especially cooking, and extremely devoted to Kinji).
- Yamato Nadeshiko: According to Kinji, she's a perfect Japanese beauty. She's also a miko according to family tradition and practices with a katana.
- Yandere: Played for Laughs, in that she threatens "exorcism" to any girl who comes between her and Kinji (including his partner Aria).
- Yaoi Fangirl: Stated in the previews for the 11th episode that enjoys the "boys love" genre, but it was a preview so it might not be canon.
A mysterious, silent sniper and Butei High student.
- A-Cup Angst: Averted. She has basically the same bodytype as Aria, with little to no chest, but she doesn't care about it at all. In the OVA, while Aria gets infuriated at seeing how developed are the rest of female characters in comparison to her, Reki can be seen completely detached from it.
- Amazon Brigade: Her native clan, the Ulus, which descends from Genghis Khan, is composed entirely of women fighters.
- Badass Boast:"I am a single bullet. It has no heart. Therefore, it does not think. It just flies straight toward its target."
- Cold Sniper: She's hypercompetent, but seemingly devoid of human emotions.
- Emotionless Girl: As a member of the Ulus Tribe, she sealed away her emotions inside a sliver of irokane in exchange for efficiency and utter devotion to her chosen husband (i.e., Kinji).
- Famous Ancestor: Genghis Khan, who roamed 12th-century Japan as famous general Minamoto no Yoshitsune.
- Fluffy Tamer: Her bullets alone could tame a giant Central Asian wolf.
- Gratuitous Princess: When written in kanji, her name reads "Princess of Buds" and she is the princess of the Ulus clan, which descends from Genghis Khan.
- Idiot Hair: Sort of. One of her hair curls up, making it stand out atop her head.
- Improbable Aiming Skills: She can even extend the effective range of her Dragunov from its standard 800 meters to 2,051 meters.
- Leit Motif: "Reki, Happou!"
- Only One Name: She always goes under the name of Reki, just Reki. The light novels expand that she is officially registered in Butei High as Reki Yada, only that she prefers to be addressed by her given name because Yada is a pseudonym - she actually ignores her real surname herself.
- Red Baron: In the novels, she is nicknamed "Robot Reki" by other students due to her inexpresiveness.
- Rei Ayanami Expy: A blue-haired Emotionless Girl who is entirely devoted to her missions and fulfills them with clinical ability. Her name is even Reki.
- Savage Wolves: Haimaki used to be one of these but she tamed him via a bullet grazing through his spine. Now he recognizes her as his mistress, thus making him a Noble Wolf.
- Sugar-and-Ice Personality: The sugar part mostly starts to show during the Kyoto arc where she becomes independent from the "Wind" and rediscovers human emotions thanks to Kinji. However, she shows hints of her inner kindness even before that with her wolf Haimaki.
- Trademark Favorite Food: Energy bars for her, fish sausages for Haimaki.
- Wacky Marriage Proposal: She proposes to Kinji while pointing the barrel of her Dragunov to him.
- Weapon of Choice: A Dragunov with a bayonet attached on its end.
- You Gotta Have Blue Hair: Light-green hair, in her case.
Riko Mine Lupin IV
A ditzy, air-headed Butei High student (or that's what she'd have you believe) and a reliable source of information. Great-granddaughter of the legendary thief Arsène Lupin.
- Animal Motifs: Like Aria, Riko has her own share of feline characteristics, with her Cat Smile as the most evident one. Shirayuki even calls her "the other thieving cat".
- Badass Adorable: She's a competent combatant and student of Butei High and she's certainly cute but the "adorable" part is largely an act.
- Broken Bird: She's an orphan living at Vlad's mercy, brainwashed into joining I-U and attempting to slay Aria, a Holmes, in order to win back her precious rosary, her identity and her freedom... all for Vlad to extract DNA from Aria and create superior genes that allow him to evolve.
- Bunny-Ears Lawyer: She acts extremely hyper and frivolous, but she's scarily competent when she gets serious, be it in fighting or detective work.
- But Not Too Foreign: She has French blood, being from the stinking-rich Lupin family.
- Cat Smile: Which emphasizes her mischievous personality.
- Chekhov's Skill: She can imitate the voice of any person she wants to impersonate very well. This comes in handy soon afterwards.
- Defeat Means Friendship: Although she joins the Kinji-Aria team for good after they free her from Vlad's clutches, it was still after they defeated her first.
- The Ditz: She acts silly it is not nearly the truth.
- Famous Ancestor: Arsène Lupin. As such, stealing stuff is one of her forte.
- First Kiss: She shares hers with Kinji, which effectively makes it his third.
- Foil: She's the composed playful seductress, as opposed to Aria the aggressive, Hair Trigger Tempered tsundere.
- Freudian Excuse: Sick of being constantly referred to as "Lupin the 4th" by Vlad (pretending to be a relative) and treated as a defective descendant whose only worth is to serve as a womb to bear a superior 5th, Riko was forced to join I-U, hoping to kill a Holmes and finally break free of her great-grandfather's shadow.
- Gag Boobs: She occasionally makes use of her rather ample chest (for her stature at least) to "train" Kinji into activating his HSS. The latter is understandably not too enthusiastic about the idea.
- Girlish Pigtails: She keeps some of her hair tied into twintails. This is to complement the ditzy persona she cultivates.
- Good Bad Girl: A bright ray of good-natured sunshine who just happens to also be very frank and comfortable with her sexuality.
- Gratuitous French: Often uses words in French language. Sometimes it is combined with Gratuitous English.
- Holding Both Sides of the Conversation: In Episode 11, to set off Kinji's HSS, she pretended to be Aria and someone else over a phone.
- I Am Not My Father: Ultimately subverted in the end, when, after defeating Vlad, who brainwashed her into doing his bidding by hammering the title onto her, she regains her pride of her heritage as Lupin the 4th.
- Knowledge Broker: A very useful informant, as she's not only from a family of burglars, but also trained in the I-U and is acquainted to some of its members.
- Lamarck Was Right: Averted. Supposedly, Riko is a deficient version of her great-grandfather; not as impressive a thief as a Lupin should be (though not too shabby by common standards, mind you).
- Lawyer-Friendly Cameo: Her surname Mine, being a reference to Fujiko Mine from Lupin III, is an obvious implication that Riko is the daughter of Fujiko and Lupin (further supported because she is said to have learned her seductress ability, a trait of Fujiko herself, from her mother). However, as her parents are dead before the start of the series, any possibly copyright infringement is avoided by Plausible Deniability.
- Loss of Identity: She felt like she lost her self after the downfall of her family and with Vlad constantly calling her "the 4th", as if she had no name. She solves it in Volume 3 with Kinji and Aria's help.
- Lovable Sex Maniac: Cheerful, helpful in times of need, and vers perverted.
- Malicious Misnaming: She pronounces Aria's name like in French instead of the correct spelling - i.e. "'Olmès" instead of "Holmes". Well... that's the idea at least. No-one in France actually pronounces it that way.
- Master of Disguise: Riko Mine is another thief character with the ability to disguise themselves excellently. Because she is the great-granddaughter of Arsene Lupin, and Holmes's nemesis.
- Ms. Fanservice: Her mother herself taught her how to make use of her womanly charms in case of need.
- Obfuscating Stupidity: She keeps a cutesy, burikko-like act in order to hide her true personality.
- Otaku Surrogate: A huge fan of otome games and the likes, although she absolutely refuses to play any sequels to her favorite games.
- Prehensile Hair: She can use her Girlish Pigtails as extra-hands or strangling ropes, hence her sharing the nickname "Quadra" with Aria. Unlike other examples, however, this seems be actually an application of Mind over Matter powers on her hair instead of a power in itself.
- Shameless Fanservice Girl: Modesty rules are of very little concern to her. This includes forcing Kinji to... explore her uniform to get his pen back in the middle of a test.
- Shout-Out: Not only is she known as "Lupin the 4th", her last name "Mine" is the same as Fujiko Mine from Lupin III.
- Signature Laugh: Kufu!
- Tsurime Eyes: The sharp points to her eyes are mostly prominent when she gets serious.
- Third-Person Person: Except when she is serious, she will refer to herself as "Riko" because this is considered a cute affection.
- Third-Option Love Interest: She is the third major member of Kinji's harem.
- The Three Faces of Eve: The Seductress (extremely flirty around Kinji, and knows how to use her womanly charms very well).
- Trademark Favorite Food: Strawberry au lait. It causes her some... disagreements during the Koko arc where she's stuck on a seat that happens to hide the trigger for a huge bomb in the train, with an extremely pressing urge.
- Victoria's Secret Compartment: She loves hiding things sizable enough to fit between her firm and ample breasts.
Kinji's best friend from the Logi Side.
- Ace Pilot: A Rank-A driver, he boasts that he can drive or pilot anything named vehicle.
- Awesome, but Impractical: His Colt Python uses .357 Magnum rounds. It packs a lot of punch, but has small capacity and poor accuracy.
- Badass Driver: He used to act as Kinji's driver in his times in Assault.
- Bromantic Foil: For Kinji. He's much more uncouth and perverted, but still friendly.
Another of Kinji's friends and classmate in the Assault Side.
- The Ace: He's a Rank-A Butei.
- Bash Brothers: He and Kinji used to be paired together prior to the latter's transfer to Inquest. Upon returning to Assault, however, Kinji already paired up with Aria.
- Chick Magnet: He's got a lot of fangirls, although he admits he hasn't had a girlfriend yet.
- Weapon of Choice: A Heckler & Koch Mk.23 with a laser pointer.
A second-year from the Connect Side who serves as the voice behind her schoolmates' intercom when on the field.
- Not Good with People: More like unable to communicate well without her equipment. This is what's keeping her stuck as a B-Rank despite being an excellent Mission Control.
Homeroom teacher of Class 2-A and instructor of Inquest Side.
- The Cameo: She has only a couple appearances in the anime.
- Cool Teacher: Appears to be pretty good-natured, even allowing Aria to sit wherever she wants since her first day.
- Dark and Troubled Past: She worked as an amoral mercenary until a gunshot injury forced her to retire and become a teacher.
- Nice Girl: She's usually sweet and kind, contrary to what her past suggests.
- Red Baron: "Bloody Yutori" was her nickname in her mercenary times.
Homeroom teacher of Class 2-B and instructor of Dagula Side.
- Badass Teacher: She's one of the top five interrogators of Japan, able to extract information from even the most hardened offenders.
- Smoking Is Cool: Is constantly smoking.
- Torture Technician: Being an open sadist that happens to be a high-level interrogator, she has this reputation.
A scientist teacher working for the Ambulance side, as well as the housekeeper of the Kōmei mansion.
- Bespectacled Bastard Boyfriend: Evokes the archetype to Kinji, at least, during the infiltration in the Kōmei mansion. Sayonaki immediately charms Aria with some worldly flirting, which causes Kinji to become jealous and claim (probably unsincerely) he only wants to seduce her for nefarious purposes.
- Hot Teacher: All the nameless girls of Butei High seem to fawn over him, sometimes even to his chagrin.
- For Science!: He spends pretty much all of his time closed up in his laboratory.
Jeanne d'Arc XXX
A mysterious silver-haired French girl who specializes in ice-elemental combat. She's a member of Daio, the "student faction" of I-U.
- The Ace: With everything that's not drawing she excels.
- Action Girl: From generation to generation too, although she rather becomes a Ms. Exposition after her defeat.
- Born in the Wrong Century: As noted by Kinji, Jeanne belongs in a previous century. She's refined in personality, wears plate mail, wields a zweihander (two-handed sword), doesn't know what a vending machine is, and dislikes skimpy clothing (including modern school uniforms, even her Butei uniform). This may have stemmed from growing up without seeing the world beyond I-U's auspices.
- Cosplay Otaku Girl: Thanks to fellow Frenchwoman Riko's influence, the once very conservative Jeanne is starting to collect Meido uniforms, Elegant Gothic Lolita outfits, etc.
- Defeat Means Friendship: While "friendship" might be an overstatement, she becomes an occasional but valuable ally to Kinji and co. after she joins Butei High. She hasn't completely severed her ties with IU, however.
- Elemental Hair: Has snow-white hair and ice powers.
- Famous Ancestor: Her name alone should be a giveaway already.
- An Ice Person: Outside of her fencing talents, she can also use ice magic to attack or incapacitate her opponents.
- Names to Run Away from Really Fast: She was known as "Durandal" during her days at the I-U, which is the name of her heirloom sword.
- New Transfer Student: As part of her plea bargain, Jeanne became a second-year transferee in the Informa Side.
- Terrible Artist: For all her many talents, her drawing skill leaves to be desired.
- Tsurime Eyes: Going with her harsh and serious character.
Number 2 of I-U, he's described as an immortal monster by Jeanne.
- Big Bad: For the first three light novel volumes and the anime adaptation, he is the central villain that team Aria-Kinji are trying to defeat.
- Evilutionary Biologist: He collects blood from countless people (including Butei High students) to absorb "superior" genes and evolve.
- Four Eyes, Zero Soul: Most apparent when he brutally beats Riko up.
- Magic Pants: During his One-Winged Angel sequence, his pants stay in place.
- One-Winged Angel: In the form of a giant canine beast so that he can be fought as the monster he is instead of a human looking monster.
- Split Personality: Tooru Sayonaki is not only a human form, but also a separate persona he made to meddle with humans more easily.
- Would Hit a Girl: Just see what he does to Riko in Episode 12.
An Egyptian girl specialized in curses, golems, and the mental manipulation of all sorts of objects. She seeks to become I.U.'s leader by using Aria as a bargain chip against the "Professor". She's a member of Ignatis, the "belligerent faction" of I-U.
- Amplifier Artifact: Pyramid-shaped buildings apparently multiply her magical power greatly. Hence why her personal ship is shaped this way.
- Antiquated Linguistics: Full with the pronoun "warawa", and using the copula "ja" (weirdly written ぢゃ).
- Does Not Like Men: However, if they dress like a pretty woman, she can tolerate them.
- Famous Ancestor: Cleopatra VII, Queen of Egypt, to the surprise of no one.
- Fanservice Pack: In the manga she seems to become more busty with each passing chapter.
- Healing Hands: Another one of her powers, as shown in chapter 59 when she heals Kin'ichi's heart wound.
- Oh, Crap!: She has this reaction when the Scarlet Bullet within Aria awakens.Patra: "What is that I am feeling fear ?!"
- Small Name, Big Ego: Well her ancestor is quite big, but she's clearly not among the top tier of I.U.'s members, despite all her talk about her "infinite power".
- Tsundere: For her hostility towards Kin'ichi/Kana she has an obvious crush on him/her. When they are shot in the heart by Sherlock Holmes, she flips out and breaks out of her coffins to heal them.
- Vapor Wear: It seems that way at first, but when she receives Clothing Damage it turns out she does have underwear. Their usefulness is questionable though.
An expert martial artist, weapon user and pilot from Hong-Kong who attacks Kinji and Aria during the "Waterbomb Festival" after the downfall of I-U, and then attacks Kinji and Reki during the trip in Kyoto. She's in an organisation called Lan Bang and seeks to recruit all three of them, whether they want it or not.
- The Ace: Despite being around the same age as Team Baskerville, she has already mastered all sorts of fields to an insane degree, from hand-to-hand combat to vehicles to bomb-crafting. It certainly helps that "she" is actually several people.
- Choke Holds: She can use her hair to strangle and incapacitate the enemy, and even break their neck if she wants. Kinji experiences first hand how terrifying it can be.
- Famous Ancestor: The legendary Chinese general Cao Cao Mengde. Hence why those who know her call her "Tsao Tsao", although she's adamant that "Koko" is the correct pronounciation where she came from.
- Identical Stranger: She ties her hair in the same Girlish Pigtails as Aria and is just as diminutive. According to her, it helps her in her "business" to look like her.
Vlad Dracula's daughter, who shows up during the Bandire in volume 8. She has continued her father's research about the Irokane and is just as immortal as he is, making her quite a fearsome opponent.
- Blood Knight: She said that she loves battles because they allow her to drink all the blood that she wants.
- Casting a Shadow: She can transform herself in an intangible shadow.
- Crazy-Prepared: For her battle against Kinji and Aria, she waited for the wheather to be favorable for her abilities, she chose a location that allowed her to freely use her One-Winged Angel mode, and she prepared a device that allowed her to more efficiently absorb energy from the city so to replenish her own energy.
- Daddy's Little Villain: She is Vlad's daughter, and begins to attack the gang in Volume 8-9 of the light novels.
- Energy Absorption: She can absorb surrounding electricity and turn it in energy for her attacks.
- Girlish Pigtails: She has blond twintails that end with a curl.
- Gothic Lolita: She wear pitch black clothes in gothic style.
- Healing Factor: She casually ignored being shot in the head, and she can regenerate limitlessly unless she is hit in all her 4 "weak points" at the same time.
- Hypnotic Eyes: She can command others to do what she says by staring into their eyes. How classic vampire of her.
- I Work Alone: Lampshaded by Riko:Riko: "Even after being captured and turned into a vampire by Vlad... she has fought alone, without backing from anyone."
- No Social Skills: Towards men, she has no social graces as lampshaded by Kinji.
- Red Baron: Spark Witch
- Sadist: She tried to kill a paralyzed Aria using a chainsaw, and when Riko interrupted her, Hilda said she just ruined the happiest moment of her life.
- Self-Made Man: Lampshaded by Riko, she fights alone without help from anyone.
- Shock and Awe: She can shoot out electricity at her enemies, though the drawback is that she generate too little electricity on her own, so she just manipulates it like a transformer.
- Socially Awkward Hero: Lampshaded by Kinji, who say that she blushed so easily while talking with a man because she has absolutely no experience in interacting with men because her father is the fearsome Vlad and there weren't any chances of knowing any guys.
- Voluntary Shapeshifting: She has 2 of these. The "second form" which takes after a demon and resemble a sort of werewolf (though she said she never use it because she find it ugly), and the "third form" which takes after a god and clad her in lightning.
The leader of I-U, who managed to appropriate many of the powers of its members.
- The Ace: A genius in a variety of fields, including fighting and detective work. With good reason.
- Became Their Own Antithesis: As a criminal mastermind, going by Professor and leading a evil organization, he's basically become a new James Moriarty.
- Big Bad: Of the first volumes.
- Improbably High I.Q.: His reasonning skills are so sharp that they are close to prescience, according to himself. He is Sherlock Holmes after all.
- The Dreaded: We're talking about a man who can make an organization full of monsters with their own goals stick together. Kana starts to completely panic when she senses his approach.
- Fallen Hero: In Watson's words, he was the foremost champion of law and order, now he's leading a terroist organization.
- No-Sell: He isn't blinded at all by the flash of Kinji's special bullet. That's because he's been blind for the last 50 years. Not that you would notice anything by looking at him
- Older Than They Look: He sure is a lively and youthful 150-year-old. That doesn't mean he can sustain his body for much longer.
- The Paragon Always Rebels: He was the original Butei, yet he became the leader of a terrorist organization.
- Power Copying: He can use the techniques of various members of the I-U, including the one linked to their bloodlines, like Vlad's "Demonic Flute of Walachia" or Kin'ichi's Hysteria Agonisante.
- Really 700 Years Old: Thanks to the effects of the Scarlet Ammo.
- Your Days Are Numbered: The day he appears before Aria is also the day he has predicted his own death.
Kinji's older brother who died at sea in an incident involving the Butei Killer.
- As the Good Book Says...: When attacking, he recites the Bible.
- Broken Pedestal: Kinji used to look up to him before he died and was defamed partially as a result of his hysteria mode. He remains disillusioned, even after meeting him again.
- The Mole: He is actually trying to take down I-U by creating a power vacuum though his methods are...a bit extreme
- Quick Draw: His special technique, Invisibile, consists in drawing his gun and shooting literally faster than the eye can see. Lucky Luke is currently crying in his bed.
- Weapon of Choice: A Colt Peacemaker. It's the most adapted to execute the above technique.
- Wholesome Crossdresser: He activates his hysteria mode by wearing female clothing.
An 18 year old, Japano-Italian girl who works for the Vatican and thus has a deep hatred for witches and demons, such as her archenemy Hilda Dracula. She joins the "Deen" alliance and becomes Kinji's ally during the Bandire, being friends with his "big sister" Kana.
- BFS: Her weapon of choice, which she can wield effortlessly despite her stature.
- But Not Too Foreign: Japanese through her father, but she otherwise grew up and lives in Italia.
- Church Militant: Her giant sword isn't for show. She was sent to the Bandire by the Vatican for a reason.
- Meaningful Name: The Japanese variant of her name ("Meiya") means "bright night", which fits with her Mood-Swinger personality.
- Mood-Swinger: She's a sweet and amicable girl most of the time, but will snap and ooze with murderous intent if you get on her bad side.
- Never Gets Drunk: She actually requires large quantities of alcohol to replenish her energy, which is a convenient excuse to circumvent the alcohol ban for nuns.
- All the Other Reindeer: She was continuously picked on by her fellow students, to the point that she just shut herself in her house and became a hikikomori.
- Hikikomori: Due to bullying, she decided to live withdrawn from society playing online games and only leaving the house when necessary.
- Loners Are Freaks: She lives a withdrawn life due to bullying.
- Gamer Girl: She turned to online games to escape off-line bullying.
- Red Oni, Blue Oni: She is the blue oni to Aria's red oni. While her cousin Aria is short tempered, foul mouthed, and loud, Minuet is a great deal more calm and reserved.
Aria's mother currently spending an absurdly long 862 years in prison for charges of being the "Butei Killer".
- Clear My Name: Aria's motivation for attending Butei High is to clear her of charges of being the "Butei Killer". If successful, she could shave off centuries of prison time for her, or perhaps even clear her altogether.
- Longer-Than-Life Sentence: She has to spend 862 years in prison. One of Aria's goals is to clear her name, in one scene she happily declares to her mother: "I managed to reduce your sentence to 700-something years."
- The Scapegoat: She got imprisoned because she was the prime suspect (and an easy target) even though she's innocent. There are hints that there is a gigantic case of corruption working in the background against her.
John Watson's descendant.
- Entitled to Have You: She's initially hostile to Kinji because she feels she should be Aria's partner due to their respective bloodlines.
- Shout-Out: Her name (and her alias, "L.") is a reference to another great detective, L from Death Note.
Sherlock Holmes's great adversary, leader of the Nemo organization.
- Big Bad: Of the N arcs.