Ranma ½, Vol. 1 (Ranma ½ (US 2nd), #1)

Follows the adventures of half-boy, half-girl martial artist Ranma, whose transforming gender problems began at the Accursed Springs in China when he became cursed to turn into a girl when splashed with cold water, and back into a boy with hot water.

When a panda and a girl in Chinese clothes arrive at the Tendo dojo, everyone is confused, but no one more so than patriarch Soun, who had been expecting his old friend Genma and his son Ranma, who is supposed to marry one of Soun's daughters to carry on the family business.
Turns out, Genma and Ranma have both been cursed to change shape when hit with cold water and turn back when hit with hot. What could possibly go wrong?