The G.G. Shinobi (ザ・GG忍?) is a side-scrolling action game by Sega released for the Game Gear in 1991. It was the first Shinobi game developed specifically for a portable game platform. The player controls the modern-day ninja Joe Musashi, protagonist of previous Shinobi games, as he goes on a mission to rescue four kidnapped comrades from an enemy, gaining control of the other ninjas (each with different abilities) as the game progresses in a manner inspired by Mega Man. It was followed by The G.G. Shinobi II: The Silent Fury in 1993.
Rumors of terror and destruction have made their way to Ninja Valley. The Master of the Oboro school of shinobi sends his best students to investigate the horrible tales coming from the suburban areas. They return with news of a powerful dark force that has established a base within Neo City.
The Master knows that only a warrior trained in the arts of ninjutsu can stand against this menace. One by one his greatest pupils enter Neo City to locate and destroy the source of the evil. Ninja Valley has lost contact with each of them. All are believed to be captured.
It is now up to Joe Musashi, the Red Shinobi, to carry through this dire mission. As the oldest and strongest of his ninja disciples, Musashi must use his special skills in the art of ninjutsu to free his fellow shinobi. With their combined strength, they can destroy the City of Fear.
Source: Wikipedia, "The G.G. Shinobi", available under the CC-BY-SA License.