Metroid Prime 2: Official Storyline

When Samus investigates an abandoned Federation ship on a planet named Aether, her ship is incapacitated by a freak electrical aberration in the atmosphere. Crash-landing on the planet's surface, she finds the scene of a slaughter. A group of creatures borne of darkness, known as the Ing Horde, attack her and steal a number of her Power Suit's abilities, leaving her for dead. As she soon comes to realize, the planet has been dimensionally doubled: One exists in darkness, the other in light.

The peaceful people of Light Aether, called the Luminoth, are slowly being destroyed by the Ing Horde, and the loss of their generators will mean the permanent eclipse of the planet by Dark Aether. Not only that, but Samus soon finds that something more dangerous than the Ing stalks the planet surface: A dark creature is on the loose, and growing more lethal by the minute.