A secret fighting style is the only weapon that can stop invaders.

Ninja In The Deadly Trap

During the Ming Dynasty, as Japanese pirates wreak havoc along the Chinese coast, laying waste to entire towns, a band of ninjas start appearing and target the Chinese military commander, General Chi. The Master of the Three Arts (who possesses a book illustrating various ninja techniques) is the only one who can combat this new enemy, so he pledges that his students will join Chi's army in their fight to wipe out the killers.