| SA-X | |
|---|---|
| Metroid character | |
 SA-X in Metroid Fusion | |
| First appearance | Metroid Fusion (2002) |
| Designed by | Yoshio Sakamoto Katsuya Yamano |
The SA-X is the main antagonist of the video game Metroid Fusion. She is a parasite that originally infected the protagonist, Samus Aran, as well as her Power Suit, before Samus was cured by injecting Metroid DNA into her. The SA-X later appears, having replicated her Power Suit, including all of her most powerful weapons from Super Metroid. She is pursuing Samus throughout the game, who is much weaker and thus must avoid her until she is able to fight back against the SA-X.
The SA-X was designed to mimic Samus' movements and actions, with designer Yoshio Sakamoto identifying such a concept as unsettling. The concept of being chased by the SA-X was reused in the video game Metroid Dread with the antagonists, the EMMI, as Sakamoto wanted to reproduce that tension.
The SA-X has been met with generally positive reception, praised as an iconic character as well as one of the scariest characters in video games. Her power, particularly in contrast with Samus', was met with praise, with critics identifying the chase scenes between the SA-X and Samus as the best moments in Metroid Fusion. She has also been compared to the EMMI in Metroid Dread, which were themselves inspired by the SA-X.