Metroid Fusion (Japanese: メトロイドフュージョン, Hepburn: Metoroido Fyūjon?), also known as Metroid 4, is an action-adventure video game published by Nintendo for the Game Boy Advance. It was released in North America, Europe, and Australia in November 2002, and in Japan in February 2003. The game is the fourth main installment in the Metroid series. Metroid Fusion was developed by Nintendo Research & Development 1, the same development team that created the 1994 video game Super Metroid for the Super Nintendo Entertainment System, to which Metroid Fusion visually bears a resemblance. Elements that are similar in both games include the gameplay, screen layout, and controls, albeit with minor changes.
Chronologically, Metroid Fusion takes place last in the fictional Metroid universe. The story centers around bounty hunter Samus Aran, who is sent by the Galactic Federation to the Biologic Space Laboratories space station to investigate an explosion. There, she learns that the station is swarming with organisms infected with X Parasites, virions that can replicate their hosts' physical appearances and memories, killing them afterward. Learning that the Galactic Federation plans to capture the X Parasites for further study, Samus must destroy the space station to protect the Federation from the underestimated destructive power of the X Parasites.
The game was given near-universal acclaim, receiving an aggregated score of 92 out of 100 from Metacritic. Praise focused on the action-oriented gameplay, while criticism targeted what was perceived as a lack of inspiration in the game. Metroid Fusion received several awards, including Handheld Game of the Year at the 2002 Interactive Achievement Awards, Best Game Boy Advance Adventure Game from IGN, and Best Action Game on Game Boy Advance from GameSpot. In the United States, the game sold 199,723 copies in its first month with revenues of $5,590,768, making it the month's tenth bestselling game. By August 2006, 940,000 copies of the game were sold in North America, while by November 2004, 155,000 units were sold in Japan.