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Nemesis is a side-scrolling shoot-'em-up game created by Konami and originally released in the arcades in 1985 as Gradius. Its popularity led to the game being ported to numerous consoles and computers, including the MSX in 1986, a port which was subsequently converted into a Sega Master System game without a license and released in South Korea by Zemina in 1987. Roughly half of the home ports are called Nemesis while the others stick with Gradius, the reasons for the change not being fully understood.
The Master System version of the game is identical to the MSX version, running in the graphics mode intended for SG-1000 backwards compatibility. As a result the gameplay is significantly more choppy than its arcade counterpart, and the graphics do not take advantage of the Master System hardware.
The Gradius/Nemesis would skip all Sega consoles which followed, though would eventually see a release on the Sega Saturn as part of Gradius Deluxe Pack.