Kumiko "Yankumi" Yamaguchi
Our heroine. High school math teacher and granddaughter of one of the most powerful yakuza bosses in Japan.
- Action Girl: Kumiko was trained to fight by her uncles and is very effective at it.
- Badass Teacher: Of course, since she's incredibly strong, brave, and protective.
- Distaff Counterpart: Kumiko is the Distaff Counterpart to Eikichi Onizuka. Only difference is Onizuka is a delinquent while Kumiko is the Ojou to a tough as nails Yakuza clan.
- Girlish Pigtails: Part of her playing the docile, feminine teacher.
- Hypocritical Heartwarming: She might be a jerk and regularly beat up Tetsu Asakura and Minoru Tatsukawa, but she makes it quite clear only she is allowed to do that to them. It's actually because of how far she would go to protect them is the reason they are so loyal to her.
- Hypocritical Humor: She will sometimes lecture her students against something she has done herself. When called out on it she will just tell them to shut up.
- Kicking Ass in All Her Finery: has a few cases, although this might be a subversion, as mostly those attempts don't end well.
- Large Ham: Whenever she passionately starts talking about honor and blood brothers and such.
- Love Can Make You Gonk: Kumiko does this whenever she is fawning over Shinohara. Her eyes go from their usual fixed glare to big, sparkly, bishojo-standard and can flick back and forth between panels when the situation calls for it.
- Meganekko: Kumiko tries very hard to fit this trope, but the harder she tries, the less convincing it is.
- Neighborhood Friendly Gangsters: Her and the rest of the Kurodas.
- Nerd Glasses: Kumiko's glasses are actually arguably multipurpose, and are sometimes used as Mask Power or Scary Shiny Glasses.
- Obfuscating Stupidity: She acts like a ditz to cover up her yakuza mannerisms.
- Oblivious to Love: Kumiko puts so much of herself into her work and helping her students that she doesn't notice Shin's feelings towards her at all.
- The Ojou: Kumiko's yakuza family often calls her Ojou.
- One-Man Army: She has been able to take down any opponent in front of her easily and singlehandedly. Except Yvegney.
- Scary Shiny Glasses: If her glasses go opaque, brace yourself.
- She Cleans Up Nicely: Kumiko. She wears a sweatsuit and Nerd Glasses with her hair in pig tails at school, but she's beautiful when wearing a kimono, a little black dress, or even a girlish nightgown.
- Stealth Hi/Bye: Constantly creeps out her students by just appearing along side them without them even noticing until she speaks up.
- Tomboy: Even her own Grandfather calls her one.
Kumiko's student. He quickly figures out Kumiko's background and eventually develops a crush on her.
- Amazon Chaser: Clearly gained an interest in Yankumi when she showed how tough she was.
- Big Man on Campus: Incredibly smart, popular, and athletic, he's loved by everyone in the school. Not that he cares.
- Bishōnen: Normally, this would have every female character lusting after him, but Kumiko scarcely notices and Fujiyama has her own peculiar tastes.
- Deadpan Snarker: Often.
- Distressed Dude: On occasion. He saves Kumiko just as often, though.
- Dating What Daddy Hates: Shin's police chief dad isn't too happy about his son liking a Yakuza Princess.
- Even the Guys Want Him: He has his share of admirers, within and without Shirokin.
- Jerk with a Heart of Gold: Shin is very aloof and cold, but he goes to great lengths to help and protect his friends. He even saves Kumiko a few times, though that's arguably after the probable time he started developing a crush on her.
- Likes Older Women: If his crush on Kumiko is anything to go by.
- Only Sane Man
- The Stoic: Shin very rarely changes his expression of casual disinterest for anything or anyone.
- So when he shows anger when he hears Kimiko has been tricked to get ambushed by her students, you can see why O.O.C. Is Serious Business.
- Surrounded by Idiots: He was able to convince his friends that his bruises and cuts were from a cupboard falling on him after a huge earthquake... until Minami points out that there hadn't been an earthquake recently.
- Will They or Won't They?: With Yankumi. They Do.
Teruo "Kuma" Kumai
Shin's best friend and classmate since middle school.
- The Big Guy: His nickname, "Kuma," means "bear" in Japanese.
- Book Dumb: He somehow managed to get a zero on his math test.
- The Ditz
- Even Bad Men Love Their Mamas: More rough around the edges than bad, but Kuma really loves his mother. There was even an arc in the manga devoted to Kuma considering dropping out of high school to take care of his mom, with his whole class pitching in to help so he wouldn't have to.
- Gentle Giant: After some Character Development.
- Gonk: Mildly. He drifts into Ugly Cute territory after the Art Evolution.
- Shipper on Deck: Probably the biggest supporter of Shin's crush on Kumiko.
Haruhiko "Uchi" Uchiyama
Part of Shin's circle of friends at Shirokin.
- Casanova Wannabe: He succeeds near the end of the manga because the girl thought it was cute how he would faint all the time.
- Cloud Cuckoo Lander: Mildly.
- Hair-Trigger Temper: If there's a fight involving a Shirokin student, expect Uchi to have compulsively instigated it somehow. And he will lose these fights, because he's also a...
- Miles Gloriosus
- Ugly Guy, Hot Wife: He finally gets a girlfriend late in the series, a beautiful girl named Shiori who's a horror fanatic.
Friend and classmate of Shin.
- Broken Masquerade: He's the one who ultimately outs Kumiko to the entire school, not out of malevolence, but because he was shocked. Also, it's because of him that the Laughing Church got outed as corrupt.
- Delinquent Hair: Has a tall, blond mohawk.
- Gonk: With his protuberant eyes, chubby face, and mohawk, he closely resembles a fish.
- The Hedonist: Exemplified when he gets mad that his friends are trying to get him to think about his future since he has no plans. He ends up taking up a job that earns a lot of money doing very little work without thinking about what kind of organization it might be, and gets in trouble.
Friend and classmate of Shin. Marginally more calm and thoughtful than the others.
- Never Bareheaded: He's always wearing a baseball cap.
- The Nicknamer: He was the one who came up with "Yankumi" as a nickname for Kumiko.
Kumiko's grandfather and the head of the Kuroda family and Ooedo Clan.
- Badass Grandpa
- Benevolent Boss
- Cool Old Guy
- Even the Guys Want Him: According to the Kuroda's councilor, Ryuichirou was such a man in his youth, "Even a guy could fall in love with him."
- Father to His Men
- Only Sane Man
- Papa Wolf: When Kumiko comes home extremely ill after being kidnapped by Kudou, Ryuichirou orders the destruction of the entire Nekomata kumi. The kumi had enough sense to scatter before the Kurodas came after them.
- Not So Above It All: He might be the Only Sane Man, but he can get just as emotional as the rest of the clan if Yankumi is upset.
The Ooedo Clan's lawyer.
- Bishounen: One of few.
- Distressed Dude: He gets thrown into harm's way quite a bit.
- Non-Action Guy: Shinohara is the only man in this series who can't hold his own in a fight. He got in trouble with some gangsters he was still in college and had to be rescued by Ryuuichirou, Kumiko's grandpa.
- Obfuscating Stupidity: You may think Shinohara completely doesn't notice Kumiko's verrry obvious crush on him. You would be wrong. He has his reasons, though.
- Oblivious to Love: Or so it would seem.
- Only Sane Man
- Will They or Won't They?: With Yankumi. They Dont.
Kyotaro "Kyo" Ooshima
The young boss of the Kuroda group.
- Big Brother Mentor: He acts as this toward most of the Kuroda group, but especially Kumiko. He was the one who taught her how to fight. He also tries to be this to Shin, though Shin is strongly against it.
- Boisterous Bruiser
- Chivalrous Pervert
- Jerk with a Heart of Gold
- Kavorka Man: He's approaching middle age and it shows, but somehow women are all over him.
- Large Ham: KNOW THAT YOU HAVE BEEN DEFEATED BY ORE-SAMA!
- One-Man Army: He is the man who taught Kumiko how to fight, after all.
Tetsu Asakura and Minoru Tatsukawa
Kumiko's "younger brothers." You rarely see one without the other.
- Animal Motifs: Tetsu is sometimes referred to as "octopus," Minoru sometimes as "squid."
- Face of a Thug:Kumiko: Stop crying! You both have faces that could kill a cow!
- Fat and Skinny: Tetsu and Minoru, respectively.
- Ugly Cute: At least Kumiko thinks so.
- Younger Than They Look: They are 22 and 21 years old. Just a year and two years younger than Kumiko.
Female music teacher at Shirokin.
- Big Breast Pride: Apparently she's an F-cup, and she doesn't mind people mentioning it. She also drew herself with Gag Boobs on her flyer for her choir club.
- Buxom Is Better: The students of Shirokin certainly think so.
- Dark and Troubled Past: During her previous teaching job at a middle school, one student attempted to commit suicide due to bullying, and Fujiyama, as his teacher, was blamed for not noticing it. She went on an aimless journey (i.e. she took a vacation), and since then has been determined not to let the same thing happen to one of her students again.
- Ephebophile: She jokes about it, but she might not be serious. She does like her boys young and thin, though.
- In Love with Love: She claims she used to be called "Love's Busty Savior."
- Must Have Nicotine: Rarely seen without a cigarette.
- Shipper on Deck: For Shin and Kumiko.
A teacher sent by the chairman to spy on Kumiko.
- Butt Monkey
- Camp Gay: He becomes this after he gets some Character Development and forms some kind of weird club with two Camp Gay freshmen.
- Ephebophile: Played for creepiness.
- Sadist Teacher: Combined with a literal BDSM fetish. He tries to force Shin to become his "pet".
- Scary Shiny Glasses
A Shirokin student who was expelled in his third year for bullying.
- The Bully: What he was when still in school.
- Boxed Crook: A variation; After he fails to kill Kumiko a third time, he's captured and brought back to the Ooedo compound, where he's kept as a servant. This is to reform him, and he actually does get a lot better because he realizes the Kurodas are keeping him in to protect him from all the people he's angered.
- Ineffectual Sympathetic Villain: He goes up against Kumiko three times and fails three times.
- Schoolyard Bully All Grown Up: Not all that grown up, but even after being expelled from Shirokin, he's fixated on continuing to make the students' lives a living hell.
Kudoh's right hand man from Shirokin.
- Arrogant Kung-Fu Guy: His ideology is, "The weak must obey the strong."
- Berserk Button: Insulting his looks is asking for an ass-kicking.
- Big Ol' Unibrow:
- The Ditz: He is apparently so dumb that he couldn't remember what class he was in and unwittingly dropped a year to be in Kumiko's class.
- The Dragon: To Kudoh.
- Dumb Muscle
- Punch Clock Villain
Gonzou Shirakawa (The Principal)
The short, bald principal of Shirokin.
- Accidental Pervert: He sometimes forgets to put his pants on before letting people see him.
- Cloud Cuckoo Lander: He does a lot of silly things, like putting on a magic show for some visiting teachers, or posing dramatically while saying something cool-sounding.
- Dirty Old Man: He sometimes drools over Fujiyama or lets slip something perverted.
- Reasonable Authority Figure: As troublesome as the students of Shirokin are, he still believes in them and backs them up.
- Obfuscating Stupidity: He knew full well that Yankumi was a Yakuza Princess and hired her because of that, knowing full well someone like her wouldn't be pushed around by juvenile delinquents.
Goro Sawatari (The Vice-Principal)
Has much more involvement in the anime than in the manga.
- Adaptational Villainy: In the anime.
- Ascended Extra: Again, in the anime.
- Asian Buck Teeth
- Reasonable Authority Figure: He becomes this in the Shibata arc and concedes that Kumiko's unorthodox teaching methods are sometimes effective.
- Non-Giving-Up School Guy: He's desperate to make Shin take the entrance exams for prestigious universities in order to raise Shirokin's reputation. He's apoplectic when he hears Shin doesn't want to go to college.Vice-principal: FINE! I'LL GET A HOLD OF HIM AND PERSUADE HIM MYSELF! *leaves office* Shawada-kuuuun! <3Fujiyama: Oh my... Poor Sawada Shin.Kumiko: It's all right. He won't be caught.
Kumiko's dog. Half Tosa dog, half... horse?
- Ascended Extra: He shows up for some silliness in bonus chapters and occasionally provides some help in the manga, but in the anime, he shows up every single episode and even has some important acting and speaking roles (though no one can understand him except the audience).
- Funny Animal: In the anime, it's almost as if he's a human in a dog's body.
- Half-Dressed Cartoon Animal: In the special chapters of the manga, he wears a sweatsuit jacket similar to Kumiko's, though when he shows up in the main story, he's naked except for the ribbon on his tail. In the anime, he wears the jacket all the time.
- Intellectual Animal: In the anime, where you can hear his thoughts.
- Interspecies Romance: It's unknown who Fuji's father is, but judging by his tail, many have presumed it was a horse.
- Talking Animal: Only to Shin in the special chapters of the manga. To everyone besides Shin, it just sounds like barking. Even outside the special chapters, though, Shin seems to know what Fuji is thinking.