While training in China at a legendary training ground called Jusenkyo, the teenage martial artist Ranma Saotome and his father Genma suffer a bizarre accident. They fall into the fabled cursed springs, and from that point on, cold water triggers a shocking transformation: Ranma turns into a girl, while Genma becomes a giant panda. Only hot water can reverse the change and return them to their original forms.

After this mishap, father and son travel to the Tendo family dojo in Japan, where Ranma discovers that his father has made an old promise. To unite their martial arts schools, Ranma is betrothed to one of Soun Tendo's three daughters. The girl chosen as his fiancée is the youngest, Akane, a headstrong and skilled martial artist who claims to hate men. Despite their immediate mutual irritation, constant arguments, and Akane’s understandable confusion over Ranma’s curse, the two are thrown together in a chaotic living situation, forced to navigate an arranged engagement neither of them wanted.

The world of Ranma ½ quickly expands beyond the Tendo dojo and the halls of Furinkan High School. The couple attracts a host of eccentric rivals and love interests. The kendo captain Tatewaki Kuno, who calls himself the "Blue Thunder," relentlessly pursues both Akane and Ranma’s female form, unaware they are the same person. Ranma’s primary rival is Ryoga Hibiki, a powerful martial artist with a terrible sense of direction, who is also cursed to turn into a small black pig named P-chan. Ryoga harbors his own secret feelings for Akane, complicating matters further.

The cast expands internationally when Shampoo, a warrior from a Chinese Amazon village, arrives in Japan. Defeated by Ranma in his female form, she is forced by village law to kill the girl who beat her. However, after tasting defeat at the hands of his male form, her duty changes to love, and she declares Ranma her husband. Shampoo has her own curse, turning into a cat, and is constantly followed by her nearsighted and jealous fiancé, Mousse, who turns into a duck. Other fiancées soon appear, including Ukyo Kuonji, Ranma’s childhood friend and a master chef of okonomiyaki, and the elderly martial arts master Happosai, the lecherous founder of the "Anything-Goes" school, whose arrival only adds to the pandemonium.

While the series is largely episodic, it features notable recurring story arcs. Early arcs establish the main cast and their curses, such as Ryoga’s introduction and the arrival of Shampoo and her great-grandmother Cologne, who often tests Ranma with impossible training regimes. Later arcs explore specific challenges, such as the battle for the Breaking Point technique on Mount Horai, the confrontation with the legendary Phoenix King Saffron, and storylines involving Ranma’s mother, Nodoka, who believes her son must live by a strict code of manliness. Despite the constant chaos, magical artifacts, and martial arts battles, Ranma and Akane's relationship slowly evolves. While they rarely admit their true feelings, they consistently fight to protect one another, and the series concludes with their engagement still in place, the curse still active, and their future together as uncertain and lively as ever.