Shadow of the Ninja, originally released in Japan as Yami no Shigotonin Kage and later released in Europe and Australia as Blue Shadow, is a side-scrolling action game developed by Natsume for the Nintendo Entertainment System (NES) in 1990. The game revolves around a pair of ninja sent to assassinate a dictator in a futuristic version of New York City. A port was planned for the Game Boy, but was released in a rebranded form as Ninja Gaiden Shadow.

Ninja Gaiden Shadow, released in Japan as Ninja Ryūkenden GB: Matenrō Kessen and in Europe and Australia as Shadow Warriors, is a side-scrolling action game released for the Game Boy in 1991 by Tecmo. It is a prequel to the NES Ninja Gaiden trilogy.