Known as "The Black Rose" (黒薔薇の小太刀 Kurobara no kodachi?) in the gymnastics community, Kodachi is presented as Tatewaki Kuno's sister and a student at St. Hebereke's School for Girls (St. Bacchus School for Girls in the manga). This is in contrast to her brother and several members of the regular cast, who attend the co-ed Furinkan High School. As a master of Martial Arts Rhythmic Gymnastics and captain of the school's team, she often preemptively attacks her opponents with various weapons, including swords or a giant mallet to cripple them, thus winning by default. She calls it "fighting in all fairness before the match." Kodachi had seldom, if ever, lost a match before battling Ranma as a result of this practice. When these failed, she has also resorted to the use of more devious methods, once attempting to shake her foe's hand with thumbtacks between her fingers. She is especially fond of using paralysis gas and sleeping powders on people, even when she has no apparent motivation to do so.
Kodachi becomes enamoured with male Ranma after the latter acts as her 'knight in shining armour' by saving her from falling off the roof of the Tendo Dojo. Unbeknownst to her, he did so after he accidentally hit her with a tea kettle while chasing Ryoga Hibiki (who was in piglet form at the time). Therefore, she is the only one of his suitors without some official or semi-official claim to him. Despite this, she considers him her lover and wants to make him her own through any means necessary. She and her brother have 'opposite' perspectives regarding this matter, since he despises Ranma's male form due to the latter's engagement to Akane and for 'enslaving' the mysterious 'pigtailed girl.' Correspondingly, Kodachi dislikes Ranma's female form, whom she believes to be a romantic rival. Regardless of his dislike for Ranma, Tatewaki has enthusiastically given them his blessing to go steady since this would free Akane for himself. He secretly imagines that they would have a miserable life together.
Unlike his other suitors, Kodachi is not actually betrothed to Ranma. Since there is no formal engagement involved in her relationship with Ranma, he usually brushes her off more often than his three fiancées. She resents this and responds with more poisons and other foul tricks. Though she has stated that she's actually aware that Ranma doesn't love her, she simply refuses to let that get in her way. She thinks he will eventually give in if she continues to make an effort.
She is a good cook who prepares elaborate meals that seem to be based in French cuisine. In one story, students who consumed her cookies described them as delicious—before they fainted because she had laced them with sleeping powder. She uses her culinary expertise to her advantage by placing poisons, toxins, serums, and other strange substances in her victims' food to attain something she wants from them, especially when Ranma is involved.
She apparently has a strong flair for the dramatic. When entering and leaving a scene or leaping throughout the city, she is regularly accompanied by a small stream of black rose petals billowing about her, complemented by a shrill, maniacal cackle that is one of her trademarks. But if she has to or otherwise feels like it, Kodachi is more than capable of acting like a perfectly well-mannered lady, and a first class host.
Like her brother, she is unaware of Ranma's curse and views his same-gendered form (in this case, the girl) as a rival for the affections of his opposite-gendered form (in this case, the boy). In the anime at least, unlike Tatewaki, this can be attributed to simple ignorance of Jusenkyo curses rather than outright denial, as she has not seen Ranma change forms in this continuity. However, in the manga, she has watched Ranma transform from male to female and not recognized what just happened, immediately asking "the pig-tailed girl" what she did with Ranma. This may imply that, like her brother, she has come to hold the idea (due to lack of explanations about Jusenkyo) that her "enemy Ranma" can somehow whisk her "beloved Ranma" away by magic.
Kodachi seems to enjoy spending time in the extensive gardens of the Kuno estate, particularly near the large pond, where she keeps her giant pet crocodile, whom she has lovingly named Mr. Turtle (or Mr. Green Turtle in the anime, occasionally referred to as "Mr. Scaly Green" in some episodes of the dub).
As her brother has expressed, Kodachi's manga incarnation is shown as quite twisted. She's been more than willing to ambush and beat up rival schoolgirls, and use potentially lethal weaponry during her matches. She also enthusiastically attempted to murder Nabiki or Hinako Ninomiya, when Ranma was engaged to the former (though this never occurred in the anime version of that same story), respectively suspected he was attracted to the latter, and was completely unconcerned about killing an innocent bystander on the off chance that he'd be Asuka's 'boyfriend.' She's been relentlessly vengeful against her brother. Simply for destroying one of her many Ranma posters, she paralysed him, then tied him up and threw him into a basin containing her crocodile. She's repeatedly attempted to use similar anaesthesia against male Ranma, in order to force her attentions on him, and also assaulted a crowd of romantic couples in this manner, with the stated reason being simple entertainment and because she viewed them as "bugs". Nevertheless she is not completely unreasonable as she was perfectly willing to return Kuno's album of pictures of Ranma's female form if he simply apologised to her for destroying the aformentioned picture.
However, her anime counterpart isn't completely heartless. In "Genma Takes a Walk" she provided Ranma and Genma with free room, board, and food when they were kicked out of the Tendo house, and in "Dear Daddy...Love, Kodachi," she was also shown to truly care for her brother and father. The former used to be a stand-in at her school parent's meetings, and she was eager to meet the latter when informed that he had returned from his long trip abroad. Curiously, she never shares a scene with her father in the Manga.
Of interesting note is that Kodachi has been bitter rivals with another girl, Asuka Saginomiya, AKA the White Lily, since they both were six years old, and violently assaulted each other's claimed "boyfriends" until only one of them was conscious. Since Kodachi 'won' the competition they agreed to compete again ten years later. Asuka has a largely similar personality, being haughty, eccentric, showy and ruthless, but seems somewhat less extroverted and more refined, if a bit snobbish. She also enjoys using explosives to defeat her foes. In their most recent battle, Akane allowed Ranma to pose as Kodachi's beau, since she was insulted by Asuka's dismissive attitude towards him. The match ended in a draw, as it was revealed that Asuka's more handsome date was simply someone she struck down just previously.
Kodachi is the only one of the fiancees that has ever admitted that she knows Ranma doesn't love her and just likes pretending that he does. This occurred during the Asuka storyline. Also, compared to Shampoo and Ukyou, her arrival at Ranma's and Akane's surprise and failed wedding was much less violent. The other two brought exploding food, while Kodachi arrived in a wedding dress.
Kodachi and Tatewaki share a dysfunctional, but caring relationship between each other. When it's revealed that the two are related after the former challenges Akane to a fight for Ranma, Tatewaki admits that she is completely insane, but tells Ranma to take care of her, and would even allow Ranma to date her. Kodachi refers to Tatewaki as "big brother" and would have him come to her school for Parents Day.
Upon their meeting, Kodachi instantly tried to seduce Ranma, much to his chagrin, and ultimately failed when met by a kick courtesy of Akane Tendo. She is completely infatuated with him, and like Shampoo, will go to any lengths to be with him, albeit her methods are usually more extreme (i.e. blackmail, paralysis powder, etc.) Ranma doesn't reciprocate any of these feelings and believes her to be a psychopath and most likely, more of a nuisance then Shampoo was.
Because of their rivalry over Ranma and the Martial Arts Rhythmic Gymnastics challenge, Kodachi seems to hate Akane and has tried to kill her multiple times. Akane, also hates Kodachi and like others, believes her to be crazy.
Kodachi is an expert in Martial Arts Rhythmic Gymnastics, making her skilled in acrobatics and weapon use in the form of ribbons, balls, clubs, hoops, and ropes, although her ribbon is her most commonly used weapon. She is incredibly agile and will typically make an aerial entrance or exit. A very cunning individual, she is not averse to using unorthodox methods in combat such as rigged weapons, explosives and various poisons. In competition, certain techniques of hers were construed as cheating, like using hidden spikes in her club. But she used them so skillfully that the judge couldn't notice them when pointed out. Her teammates also had to leave after being discovered to be helping her move the arena. On the other hand, disguising a steel rod as a rope, or throwing her brother at Ranma, were within the main framework, which simply prohibits barehanded attacks. Kodachi has been shown to wear her characteristic leotard under virtually all her clothing, presumably because it permits a superior range of motion while in combat.
Compared to the rest of the regular Ranma cast, Kodachi has apparently been treated as roughly equivalent to Ukyo or Shampoo during free-for-alls gang-ups aqainst Ranma, Hinako or Genma, outside of "Martial Arts Rhythmic Gymnastics" tournaments (within these constraints she came close to defeating Ranma, as he/she was early in the series, before Cologne's power-up, and limited to non-barehanded attacks), and seems to have superior recovery time, as the latter two took considerably longer when drained by Hinako. However, any actual semi-confrontations during these situations have been limited to a few panels, alternately been completely off-screen, so it's very hard to draw a conclusion on these merits alone. More importantly she has also been able to fight / parry with Tatewaki on even or slightly superior footing, but it's unclear whether he held back or not (as he seems inclined to do against females).
- Black Rose Blizzard: Kodachi's most commonly seen technique, typically used for her exits. Using her ribbon, she generates a storm of black rose petals, which can also be used to screen an escape.
- Paralysis powder: One of Kodachi's trademarks, capable of incapacitating anyone. She has slipped the powder into tea or distributed it via bouquets of black roses.
- Rose bombs: Bombs in the form of black roses which are thrown like darts.
- Her distinctive noblewoman's laugh is similar to several other characters: Naga the Serpent from Slayers, Ayeka from Tenchi Muyo!, Nanami Kiryuu from Revolutionary Girl Utena, and Zoisite, Esmeraude, Kaorinite, and Fish Eye from Sailor Moon.
- She bears a superficial resemblance to the demon bird Abi from InuYasha. Both have long black hair (although, Kodachi wears hers in a side pony tail), and possess similar facial designs. Both characters also have identical shades of lipstick, and the same voice actors in both the Japanese and English language versions of their series.
- She is somewhat similar to Ryoko Mendo from Urusei Yatsura. They are both rich, have annoying older brothers, long black hair, and can act proper and sophisticated while also possessing a sadistic, murderous streak. However, Ryoko is far more manipulative.
- In every one of her appearences, it is revealed that she always wears her famous green leotard underneath whatever she is wearing.
- She is Ramna's only suitor who has not hit him, although she does attack him in one of the intros.
- She is the only recurring suitor of Ranma and Akane to not have had an alternative love interest.