is a series of video games by
Tecmo featuring the
ninja Ryu Hayabusa as its protagonist. The series was originally known as in Japan. The word "
gaiden" in the North American
Ninja Gaiden title means "side-story" in Japanese, even though the
Ninja Gaiden series is not a spinoff of a previous series. The original arcade version, first two
NES games and
Game Boy game were released as
Shadow Warriors in
PAL regions.