Galactic civilization has peaked. Peace reigns throughout star systems, trade lines run unhindered, and the numerous species of the universe live in harmony.
Unfortunately, the peace didn't last. Innocent lives came under fire from Space Pirates - a group of alien beings literally bent on looting trade ships and inflicting as much devastation as possible. The Pirates quickly made a name for themselves by raiding trade ships and leaving their occupants stranded in space.
The Galactic Federation - the governing body of the united galaxy - fared little against the chaos. The Space Pirates continued to wreck havoc unchecked, eventually raiding and annihilating the human colony K-2L.
Against all odds, a lone human child survived the carnage. Members of the Chozo race - wise and ancient bird-like beings - arrived at the site and rescued the three-year-old girl: Samus Aran. Giving her a new home among their kind on planet Zebes, the Chozo gave Samus a new purpose in life. Training her in their ancient art of combat, the Chozo honed Samus' skills and built her a custom Power Suit to one day take the fight back to the Pirates.
Years later, long since Samus left Zebes for the stars, the Pirates revealed the full extent of their treachery. Assaulting Zebes and forcing the remaining Chozo population into exile, the planet quickly fell into enemy hands to serve as their new fortified base of operations.
Despite delivering blow after blow to the beleaguered Galactic Federation, the governing council managed to keep their operations afloat. But the Pirates had recently acquired a new trump card. Raiding a secret Federation scientific expedition tasked with exploring the remote world of SR388, the Pirates acquired a new prize: the scientists had discovered a previously undiscovered lifeform known as Metroids.
These parasitic beings proved almost as dangerous as the Pirates themselves. Capable of draining the life force from any hapless victim, the simple-minded Metroids gave the Pirates all they needed for galactic domination.
Securing their Metroid specimens deep within Zebes, the Pirates began multiplying the parasites alarmingly fast. With little options left, the Galactic Federation hired a respected bounty hunter - a now fully matured Samus - to infiltrate the Pirate's fortress on Zebes, eradicate the threat they posed and ensure their Metroid army never leaves the planet.
Her mission is ultimately three-fold: protect galactic civilization by striking at the heart of the Pirates, honour the Chozo legacy within herself, and avenge the loss of her parents all those years ago...