Metroid Fusion is a video game starring interstellar bounty hunter Samus Aran. While on a mission to support the planet SR388, she is attacked by an X parasite which has the ability to mimic her abilities. Fortunately, she is saved by a vaccine made from the DNA of the last Metroid - the only predator of X parasites. When they spread to a research station orbiting around SR388, Samus must fight them all or be killed trying.