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, "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. The series gained popularity on the NES for its tight action-platform gameplay, catchy music and, according to G4's X-Play, for being the first console game to have the story presented in cinematic cutscenes. The 8-bit trilogy was enhanced for the 16-bit Super Nintendo Entertainment System in 1995. Sega released two Ninja Gaiden games for the Game Gear and Master System, the latter only for PAL regions. The original series' setting of said universe is a retro-futuristic version of the 1980s. A new game, titled Ninja Gaiden, was released in 2004 as a 3D action game on the Xbox, developed by Team Ninja, the makers of Dead or Alive. The Ninja Gaiden franchise is known for its high degree of difficulty, particularly the original NES version and the Xbox revival. According to Eurogamer, the gameplay of the Strider arcade franchise was a vital influence on the modern incarnation of the Ninja Gaiden franchise.