The SA-X is the main antagonist of the 2002 action-adventure game Metroid Fusion. It is the mutated armor of Samus Aran that was possessed by an X-Parasite, who searches for her throughout the Biologic Space Laboratories in an attempt to kill her.

^ Adam: You know that the X reproduce by asexual division. Because of this mechanism, there are now no fewer than 10 SA-X aboard the station. Nintendo R&D1. Metroid Fusion.

Concept and creation. Conceived by scenario designer Makoto Kano and designed by Hiroji Kiyotake, series co-creator Yoshio Sakamoto conceived of the idea of making Samus a woman midway through the first Metroid's development, which the development team voted in favor of.

Remember, the X and Metroids are "natural" enemies. In Fusion, the SA-X was willing to die in order to destroy the Metroid lab and an X core willing to blow up BSL along itself. Later, a SA-X "saved" Samus from the Omega Metroid which in reality was just a self-preservation method.