Once upon a time in Japan, there was a band of great Ninja warriors led by Yamata called Iga Ninja. One day they witness a flash in the sky and a roaring giant ball of fire crashes into the distant forest. The warriors rush into the deep woods in an attempt to identify the mysterious fireball. There, instead of finding predictable enemies, they are stunned to face never-seen-before creatures with claws and fangs, the aliens! The hungry brutal aliens start to savage and feast on the Ninja warriors, leaving only a few to survive. Yamata and his warriors swear to avenge their comrades deaths and risk their lives to challenge the aliens. However, none of the Ninja weapons, neither their swords nor their throwing stars, has any affect on the alien warriors.