"Ninja Gaiden (NINJA 外伝) is a series of video games by Tecmo featuring the ninjaRyu 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, though the Ninja Gaiden series is not a spinoff of a previous series." Ninja Gaiden - Wikipedia
Actually, two Ninja-Samurai jumping into the air at each other at midnight in Japan at clear moonlight with Katana unmasked reverberates with the Superconscious as well the Heart.