SR388 is a key location in the Metroid game universe. Long ago, an ancient race known as the Chozo colonized this planet only to find themselves threatened by the numerous violent creatures indigenous to that world. Chief among these many hostile creatures were the deadly X Parasites: highly virulent organisms that spread across the planet like a plague and wiped out everything in their path. To combat the X, the Chozo engineered their own breed of biological weapons: Metroids. The Metroids were successful in exterminating the X Parasite, but in doing so they rose to the top of the food chain on SR388. With the Metroids now the dominant predators of SR388, the Chozo abandoned their colony and disappeared to parts unknown. Centuries later, the Galactic Federation would discover SR388 and the Metroid parasites that lived there. The Federation recognised the threat that Metroids could pose were they ever to be taken off-planet and marked the entire species for extermination.
The Galactic Federation hired bounty hunter Samus Aran to land on SR388 and carry out the extermination of the Metroid race. Samus succeeded in wiping out all but one infant Metroid, which seemed to mistake her for its mother. Samus took the creature with her when she left the planet.
In Metroid Fusion, Samus led a Galactic Federation research team on the surface of SR388. While there, she encountered a mysterious, parasitic organism which entered her body. She later discovered that the organism was an X parasite, an organism which attacked living creatures and copied their DNA. The planet would later be destroyed when Samus changed the orbit of the research station to impact it in an attempt to eradicate the X parasites.