Genma is Ranma's insensitive, selfish and greedy father. He originally took Ranma to Jusenkyo because he'd heard about it in a Chinese brochure even though he can't read a word of Chinese. He also got cursed, turning into a panda. Unlike Ranma, he doesn't have much trouble with it, especially because he can get away from his problems in his panda form. While Genma frequently preaches duty and honor as a martial artist, he seems to be a poor example to set those standards by. For all the wrongs he has committed, he usually tries to get Ranma to shield him from the consequences whenever any of those actions catch up with him. While he's usually either too lazy or scared to show it, he's an incredibly powerful martial artist, who invented the Umisen-ken and Yamasen-ken and possesses a towering battle-aura.

Soun is the head of the Tendo household and one of the two families to practice Anything Goes Martial Arts. He is also a widower, left to single-handedly take care of his three daughters. He has a large house that is occasionally in need of repairs due to the fights that take place. While he owns his own dojo, students have not been explicitly shown. Oddly he may not have a recurrent source of income and, in the anime, spends most of his time playing Shogi (Japanese chess) with his old training partner Genma. Community representatives frequently approach him when they have problems with unusual phenomena, so this may provide some of it. However he is shown to be quite careful with the expenses and gets upset when Nabiki spends his savings on expensive gifts, or when Ranma throws the dinner on the floor. Soun is anxious for his daughter to say she loves Ranma, or the other way around, to continue the legacy of his school. He'll start announcing wedding plans if Ranma and Akane seem romantically involved. Soun is able to manifest himself as a ghostly, floating oni head, whenever he is upset. He generally assumes most incidents are Ranma's fault. He's shown as extremely protective of his children, especially Kasumi, and becomes sad if their affection is in doubt. Miss Hinako is attracted to him, but he is very loyal to his dead wife and visits her grave in memorial.

Mousse is a long-time friend of Shampoo, though she might not view it that way. He has been in love with her for most of his life, but she finds him annoying at best. He can't see very well without his glasses, often mistaking someone for something else! He comes to Nerima in search of this "new fiancé" that Shampoo has, and he stays to attempt to woo his sweetheart. Shampoo rebuked his advances when they were children and this still holds true by Amazon law, even if he manages to defeat Ranma in combat, but he remains persistent. Now a waiter at the Cat Café, he turns into a duck thanks to his own Jusenkyo curse. When in human form, his clothes contain weapons of drastic proportions, including needles, chains, swords, and just about anything else imaginable. In duck form, Mousse can hide knives in his feathers.

Tatewaki Kuno is an upperclassman at Furinkan High and was the big man on campus – at least until Ranma came along. Hailing from a very wealthy family, he is also captain of the kendo club and wields both his fortune and sword with equal ease. Given to spouting off Shakespearesque poetry (he quotes Confucius in the Japanese original), he is madly in love with Akane. He also falls for Ranma’s female half and never realizes that she is really his mortal enemy in girl form. He once overhears her called by name, and attempts to write it down for future reference, but never makes a connection and continues to refer to her as a "goddess in pig-tails" for the entire series.

Dr. Tofu is the resident chiropractor and well-liked by the residents of Furinkan. He is also a martial artist, though never seen practicing, and is quite competent at tending Ranma and Akane in their various scrapes. He is also madly in love with Kasumi and becomes quite dangerous (albeit unintentionally so) when she is around. In these instances, he becomes an incompetent fool, sometimes harming his patients. Sadly, she doesn't feel the same way. He always seems to know what to do—until Kasumi arrives. The anime gives him a larger role, though in both mediums, he becomes a very minor character after the first few stories.

The very definition of a dirty old man, Happosai is the grandmaster and founder of the Anything Goes Martial Arts school. Genma and Soun were his original disciples, but they got fed up having to steal lingerie for the old lecher and decided to try and finish him off. They were quite surprised when he showed up many years later to make them miserable and find a successor in the Art. Unfortunately for Ranma, he was the incorrigible old freak's choice. He is an immensely skilled and powerful martial artist, with but one weakness: bras and panties. Happosai is so obscenely addicted to his perversion that he suffers from withdrawal if he goes without them for an extended period. It seems as though he always shows up at the most inconvenient moments. Happosai can go to great lengths to ruin the life of anyone that displeases him, but usually chooses silly methods. He nonetheless shows a soft spot for children.

Akane is Soun's youngest daughter at age 16. She is a very insecure, awkward and sensitive girl with a hot temper and a big heart. After first encountering Ranma's male form as a naked stranger in the bathroom and becoming further upset by his insults, the engagement isn't off to a good start. With time, both Akane and the relationship mellow out, and she helps or risks her life for Ranma on several occasions. Akane regularly feels inferior to Kasumi in beauty and feminine pursuits, to Ranma and his other fiancées in cooking, martial arts ability or gymnastics, and to other students in swimming. She is trying hard to excel in everything, but is either clumsy or completely inept at all except for schoolwork and certain sports activities. When someone, frequently Ranma, belittles her lack of success, or calls her ugly, over-muscled, unfeminine and tomboyish (which she agrees with, but has complexes about) she often gets upset. She is shown as very friendly towards people who are polite and don't insult her and has consistently risked herself to help or save Ranma.

Ten years ago, on a training trip in the country, Genma stole Ukyo's father's okonomiyaki yatai (food cart), leaving her behind and breaking the arrangement he and her father made. However, before this Ranma and Ukyo were friends, though Ranma never knew she was a girl. Shamed and ridiculed by her peers, Ukyo decided she wouldn't like boys, dressed and lived as one, and devoted herself to okonomiyaki-style martial arts. After a heated battle, Ranma discovers her true gender. Meanwhile, she discovers that he does not get along with his "uncute" fiancée Akane. They reconcile, and she falls in love with him again. Ranma still treats her as only an old friend, and her plots to win him over have been almost consistently non-violent, unlike those of his other suitors. She has been willing to give up her house and restaurant, or rescind her craft for Ranma's sake, if it would mean that they could be together.

Nabiki is the middle daughter of Soun. She loves money above all else and is willing to sacrifice anyone to gain more of it, even ruin her family to win a bet. In most stories that she plays a vital role, she either attempts to extort money from someone, or sets up dangerous situations for her own amusement, or both in combination. In different translations, she has been outright stated to have 'no maidenly feelings' or be 'completely heartless', but she isn't above using her classy and highly attractive appearance as a lure for potential suitors/victims. She has a sarcastic, materialistic, egoistic, manipulative, sadistic and completely amoral attitude that is a sharp contrast to her older sister. Nabiki has been stated to invest at least some of her earnings in personal stocks, but is extremely unwilling to spend her own money. She would rather steal Akane's wardrobe, get spoiled by an admirer, or empty Soun's savings by buying expensive gifts for herself. She was briefly engaged to Ranma after Akane got frustrated and also played a role in bringing the two back together, when he seemed to turn into more work than her profits warranted.

Kasumi is the eldest of the Tendo girls, and the most traditional in the Japanese sense. She has graduated high school and spends most of her day looking after the Tendo household, acting as the family's substitute "matriarch" ever since her mother's untimely death; by cooking, cleaning and helping her family. Sweet, innocent, caring, self-sacrificing and seemingly unaffected by the lunacy that is surrounding her, Kasumi is one of the few characters who never gets hurt at any point in the series, if you don't count her temporary possession by a mischievous oni. She's occasionally shown as wiser and more perceptive than readily apparent, and can see through Nabiki's schemes. Beyond taking care of the household, she's been shown to go out to meet friends and has borrowed a pressure point book from her good friend Dr. Tofu, who is in love with her.

Training with Genma at Jusenkyo in China, Ranma was thrown into the Spring of Drowned Girl. He emerged as a young girl, according with the spring's curse. When splashed with cold water, he turns into a girl, but when splashed with hot water, he changes back to a boy again. Martial arts is the 16-year-old's hero/heroine's life. He also possesses a very large but easily wounded ego, believing his physical strength to be his only virtue. Whenever his pride is damaged, Ranma will go to great lengths to rectify the situation. He can come across as petty, insensitive and arrogant, as he is prone to cheat or give insults, often acts out of unthinking selfishness, and is a frequent braggart. However much of the above is caused by awkward immaturity. He's also very self-sacrificing when he needs to be. Ranma has an extreme fear of cats, resulting from when his father trained him in a dangerous technique. If Ranma is isolated with a cat in a very small space, he begins behaving like a cat himself.

Ryoga is a childhood rival of Ranma's and is famous for losing his way thanks to a horrible sense of direction. After spending months looking for male Ranma for leaving before their planned duel, he finally finds him in China but gets pushed into a Jusenkyo spring by female Ranma and now changes into a small piglet. He seeks Ranma out with a large grudge, and discovers Akane who thinks that little “P-chan” is quite cute. Of course, she doesn’t know that it’s really Ryoga, but that doesn’t stop him from falling in love with her. When not upset he's usually shy, humble and polite, especially around women. His anger lessens with time, first into a fierce rivalry, then shifting back and forth between tense competition, uneasy allies or non-serious conflicts. Finally they became on friendly enough terms for Ryoga to repeatedly risk his life to help Ranma, but the competition between the two will likely persist forever. Ryoga spends his time wandering through the wilderness, training and amassing new techniques to exceed Ranma — if he can ever find his friend and nemesis.