Metroid Fusion is the direct sequel to 1994's Super Metroid. The game begins as Samus Aran is sent back to planet SR388 to assist a Biologic Space Labs investigation team. While on the planet's surface, Samus is infected by a previously unknown parasite, known as X. The X parasite nearly kills Samus, but fortunately she survives. Shortly thereafter, an explosion rocks the Biologic Space Labs. Something has gone terribly wrong, and, it's up to Samus to investigate.
This game is similar, in terms of gameplay and structure, to the classic side-scrolling Metroid games. The game consists of a very large inter-connected environment. As Samus learns a variety of new moves and weapons, she is able to explore new areas of the Space Lab and unlock the secrets of the X parasite.