The first Metroid adventure for Game Boy Advance, Metroid Fusion, also known as Metroid IV saw Samus Aran with a radical new look.
While lending mission support to the Federation on SR-388, Samus is attacked and infected by a new lifeform Federation scientists call the X parasite, which has infected much of the creatures of SR-388. Samus is only saved from death by a vaccine made from cells from the last Metroid. The Metroid DNA changes Samus' metabolism so much that she can heal herself and upgrade by absorbing any X parasites she finds. Now the X have spread to a nearby abandoned space lab, infecting all research specimeans, including pieces of Samus' power suit, and a substantially weakened Samus must exterminate them all or die trying. But she is being constantly stalked by a advanced beast called the SA-X which not only resembles her, but knows everything about her and possesses all her weaponry...