This show is about two anthropomorphic rabbit twins named Yin and Yang that train under Master Yo, a grumpy old panda who ends up being their father. They learn the sacred art of Woo Foo, a special type of martial arts that involves might and magic. They must work together to save the world from evil villains and forces that want to destroy, corrupt, or take it over. But through all these adventures, Yin and Yang still portray typical siblings; sometimes disagreeing with each other, but still care about each other and working together needed.
During the first season, the primary goal was to defeat the Night Master, a powerful enemy. During the current, ongoing second season, Steve Marmel stated that there are four story lines. The first one is the crowning (and eventual defeating) of a new Night Master (or Mistress), which might probably be Carl as he is in the center of villains in the opening sequence, replacing the Night Master. The second is Yang's own quest to find powerful mystic artifacts by some later-revealed-to-be villains: the four evil heads who he thinks are the masters of Woo Foo. The third is Yin and Yang building a Woo Foo army to fight Eradicus. But what's the fourth...?