Sadamitsu the Destroyer(2001)

The earth is being overrun by Alien invaders and, while on a mission to stop the invaders, an assigned Attendant is injured. He seeks the help of a human named Sadamitsu. Sadamitsu makes it his mission to rid the world of the invaders, to prevent the coming of the ultimate enforcer, the Vulture. The problem is the Vulture is already here, and buried in Sadamitsu's past is the reason the Vulture hasn't already destroyed the Earth.