SR388 (sometimes SR-388, rarely SR 388) is the setting of Metroid II: Return of Samus for the Game Boy. It is the Metroid creatures' home world. The Chozo had their own civilization on the planet at one point in time. Metroid Fusion takes place in a research station in orbit around this planet.

SR388's surface is rough, dry, and rocky. This world has many dangerous creatures and killer robots. Ancient ruins can be seen in the deep caverns of SR388. Samus could not access these places until a certain amount of Metroids in the area were killed. They were blocked off by pits of damaging magma, which drained when a number of Metroids were killed. It is unknown how the once great Chozo cities were destroyed.

At the time of Metroid II, the planet is overrun with all sorts of indigenous species as well as the Metroids. Samus' mission was to wipe out every last Metroid by exploring this vast, cavernous world. It may be hard to imagine any species being able to survive very long on the Metroid's home world – it is almost completely composed of rock, and the depths of the planet are full of deadly lava. There is also intense beta radiation bombarding the planet which is believed to act as a mutagen for the Metroids, causing them to metamorphose from their simple jellyfish-like shape into even more dangerous Metroids.

Before the Chozo came to SR388, the destructive X Parasites were set to overrun the planet with their vast, insurmountable numbers. Then the Chozo arrived. To keep them in check, the Chozo created the Metroids and let them loose on the planet. The Metroids did keep the X Parasites in check very well, but when Samus Aran eradicated the species in Metroid II because they were deemed too dangerous to ignore, the X came back in large numbers. One thing should be noted, as it may be a minor continuity issue: the X Parasites are first mentioned in Metroid Fusion, but they are never seen during the course of the Metroid II game. This could just mean that the Metroids regulated the X Parasites' numbers so well that there were relatively few left by the time of Metroid Fusion. It is also possible there were no full X Parasite colonies, which made them invisible to the naked eye.

At the end of Metroid Fusion, Samus set the Biologic Space Labs (B.S.L.) station to impact with SR388, which caused an explosion that vaporized both the station and the entire planet, destroying the X Parasites in the process.

Indigenous Species Edit

Ancient Machines Edit

Machines placed on SR388 ages ago to guard its corridors.


  • Metroid (First mentioned)
  • Metroid: Zero Mission (Mentioned)
  • Metroid Prime (Mentioned)
  • Metroid Prime 3: Corruption (Mentioned)
  • Metroid II: Return of Samus (First appearance)
  • Super Metroid (Mentioned)
  • Metroid Fusion