Ranma Saotome is the son of Genma Saotome, and the central character of Ranma 1/2. He has studied martial arts under his father's tutelage since he was very young. However, his life changes forever when Genma takes him on a training expedition to China. There, they travel to Jyusenkyo, a land dotted with countless fresh water springs, under Genma's belief that it's a martial arts training ground.
Despite numerous warnings from their guide, Ranma and Genma began their training, and Ranma quickly knocks his father into one of the springs. However, when he goes to check on Genma, a giant panda emerges from the water instead and knocks him into another pool. When Ranma surfaces, he is horrified to discover that he has turned into a girl.
As it turns out, Genma, who doesn't speak a word of Chinese, didn't realize that Jyusenko is actually a collection of cursed springs. Each spring was the site of a drowning of a different creature, and whoever should fall into such a spring will take that form whenever he or she is splashed with cold water. Thus, whenever Ranma is splashed with cold water, he turns into a girl. The only way to reverse the curse is to be splashed with warm water.
Ranma's troubles don't end there. Upon returning to Japan, he discovers that his father has arranged his marriage to one of the three daughters of Soun Tendo, Genma's old friend and training partner. Ranma wants no part of it, but is forced to submit as Genma takes him to the Tendo family dojo. After an evening of great confusion involving a cold rain and warm baths, Ranma finds himself engaged to Akane Tendo, the youngest Tendo daughter, who finds the idea of marrying Ranma equally repugnant.