Tendo Soun and Saotome Genma are lifelong friends and practitioners of Anything-Goes Style of Martial Arts. Soun married and had three daughters. Genma married and had a single son.

Tendo family:
Soun, the father, is likely to cry at the least provacation. Kasumi, the eldest daughter, is ultra-feminine and takes care of the household since their mother died. Nabiki, the middle daughter, is conniving and concerned only with making the most money in the most efficient way, and cares not who gets in her way -- the only person she will not exploit is Kasumi. Akane, the youngest daughter, has always been a bit of a tomboy, but had a massive crush on the local acupressure doctor (Dr. Tofu) and wanted to be feminine like Kasumi because of that. Akane's skill at martial arts resulted in her having to literally fight off boys that wanted to date her daily at school.

Saotome family:
Unlike the Tendo family, the parents are both still alive. Genma, the father, is about as sexist as it is possible to be and not be murdered by a passing woman for his attitude (beaten up for it... often, though). Nadoka, the mother, had once commanded that the men in her family not do anything unmanly or she would call up on them to commit Seppuku (suicide by longsword through the gut), and as such Genma and Ranma were always afraid of Ranma's life being in danger if she found out about his transformations.

The Cursed Springs (Jusenkyo)
Genma took Ranma as a small boy on a decade-long training trip to China. They swam from Japan. One of the training grounds was the poles sticking out from the 1,000 Cursed Springs of Jusenkyo. Ranma knocked Genma off, as usual, but Genma was not what leapt back out of the spring he fell into, it was a giant panda. Ranma was so shocked at suddenly facing a panda, he froze, and Genma knocked HIM off. See, the springs at Jusenkyo have all had something different drown in them hundreds or thousands of years ago. Whoever falls into one of the springs then takes on the body of that which drowned in that one. Ranma fell into the spring of the drowned young girl.

The curse is activated by being splashed with cold water -- and reversed by being splashed with hot water.

Other characters besides the Saotomes that have curses include:

• Shampoo - Chinese heir to the Amazon throne, Amazon tradition says that she must kill a woman who defeats her (Ranma in female form did that), and marry a man who defeats her (Ranma in male form did that). Spring of the drowned cat.
• Ryoga - childhood friend of Ranma's who is overly dramatic about everything... everything that goes wrong is a reason to kill someone. He is eternally lost and has the worst sense of direction this side of Melanie Ezell! Spring of the drowned piglet.
• Mousse - Chinese weapons master desperately in love with Shampoo, blind as a bat without his glasses. Spring of the drowned duck (I know... I know...).

Engagement
Soun and Genma agreed when young that if one had a daughter and the other a son, they would be married and so merge the two best friends' Anything-Goes Martial Arts Schools and Legacy. When Genma and Ranma show up in Nerima (the town it is set in), Ranma is in female form, and the older sisters jokingly nominate Akane to be the designated fiancé, since she's a tomboy and not interested in boys, anyway! She then discovers Ranma's secret when she walks in on 'her' in the bath and a very male (and very naked) Ranma is stepping out. She calls him a pervert at that point, thinking him a crossdresser despite his female form being smaller and with a different colored hair. When all is said and done, Genma relates the story of Jusenkyo to the Tendos, and Akane is STILL nominated as fiancé because, "he's half not a boy!" The two are opposed to the idea of an arranged marriage, but it becomes clear early on that despite the name calling and violence between the two that they really do LIKE-like each other. He calls her uncute and a tomboy. She calls him pervert, crossdresser, dummy, etc. Ranma is much like his father (his ONLY role model) in attitudes toward women, but you can tell that he doesn't REALLY buy into it, and pays it lip service (especially when he's embarrassed).

Fiancés
Over the decade in China, Ranma accumulated a large amount of fiancés due to Genma being an idiot. Aside from Akane, the first one promised... and Shampoo, fiancé by her people's law. There are dozens others that have been promised in exchange for a meal here or there through the years. There is also Ukyou, who not dresses like a boy, but is really quite girly. The three that are the main fiancés are just those three: Akane, Shampoo, and Ukyou. Ryoga and Tatewaki (one of the upperclassmen at school) both want Akane, though Kuno Tatewaki is as interested in girl-type Ranma (and is the only person in Nerima that doesn't seem to know that the two Ranmas are the same person other than his equally deranged sister Nodachi). Mousse wants Shampoo. Tsubasa (the master of disguise) wants Ukyou. Tsubasa's typical disguise is that of a cute young girl, because that way Ukyou won't feel out of place if she decides that they can date (because she's always dressed as a boy).