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Ninja Gaiden (NINJA 外伝) is a media franchise based on action video games by Tecmo featuring the ninja Ryu Hayabusa as its protagonist. The series was originally known as Ninja Ryukenden (忍者龍剣伝, Ninja Ryūkenden, lit. "Legend of the Ninja Dragon Sword") in Japan. The word "gaiden" in the North American Ninja Gaiden title means "side story" in Japanese. The original arcade version, first two Nintendo Entertainment System games and Game Boy game were released as Shadow Warriors in PAL regions. As of 2008, the series has shipped over 7.7 million copies