X is for Xing Yi Quan
Xing Yi Quan is one of the major "internal" styles of Chinese martial arts. The style is characterized by aggressive, seemingly linear movements and explosive power. Xing Yi Quan uses coordinated movements to generate bursts of power intended to overwhelm the opponent, simultaneously attacking and defending.
The video below gives a real quick overview of the history and theory of Xing Yi and shows the movements being performed. And there's a woman demonstrating - yay!