Ninja Assault was developed by Namco, who also created the Time Crisis series; however, this game has more in common with Lethal Enforcers, Virtua Cop, and The House of the Dead series, whereby the movement is completely "on-rails" (i.e., with no hiding pedal), and the player must shoot away from the screen to reload.
Both versions of this game support up to two players in cooperative gameplay.
- Guren: Princess Koto's royal ninja bodyguard.
- Gunjo (voiced by J.S. Gilbert): Guren's partner.
- Aoi (voiced by Joanne Elefenbaum): Mysterious ninja who wants to avenge her father's death, as indicated by her deceased father's eyepatch heirloom. She only appears in extra story mode in PS2 version.
- Princess Koto (voiced by Joanne Elefenbaum): Princess of Japan, she has the ability to see in the future when sleeping.
- Shogun Kigai (voiced by Bryan Session): The evil leader of the demon army who is planning to sacrifice Princess Koto for his resurrection ritual.
- Kagenin: Loyal commander of the elite demon forces and Shogun Kigai's right hand man. He has reputable ability with the "Gun of Darkness" which he wields against Gunjo, Guren and Aoi in a stand off in Kigai's castle.
- Dragonlord: Shogun Kigai's swordsman, he was the only henchman that guarded the cave against Guren and Gunjo (Arcade Mode) and Aoi (Game Chapter Mode).
- Dragonlord (giant-snake form): Mother of Dragonlord, she was disappointed of her son that he was defeated by humans but nonetheless helps him battle against humans.
Ninja Assault is advertised in in-game email message in Namco's Xenosaga Episode I: Der Wille zur Macht.
After finishing the PS2 release of the game, one would unlock a code that could be entered in the contest at Namco's website.
The original arcade game has been received much better, with the GameFAQs average score of 8.3 based on 4 reviews.