Ranma rescues Akane, punching through the giant bolder Pantyhose Taro threw at them. Ranma makes sure Akane is alright, then turns back toward his adversary. He’s pissed. Pantyhose Taro crossed a line few dare ever cross. For Ranma, Its one thing when someone tries to hurt him, but NO ONE tries to hurt Akane.
Throwing that bolder and endangering Akane was Taro’s one mistake, that inevitably seals his fate, and assures his own defeat.