During the events of Fusion, Samus was infected by X Parasites and much of her Power Suit was surgically removed. She was given a vaccine made from the DNA of the baby that saved her life. While this meant that Samus was now completely immune to the X Parasites, it also gave her the Metroid's weakness to cold. Because of this weakness, Adam conjectured that the new Fusion Suit would reject the Ice Beam upgrade, so the Galactic Federation never tried to create a downloadable version for Samus.
Towards the end of the game, Samus defeated the SA-X, a copy of Samus born from the parts of her Power Suit that had been surgically removed after her initial infection. Before she could absorb the Core-X left behind by the SA-X, it escaped into a collapsed tunnel. As Samus attempted to return to her gunship, she was attacked by an Omega Metroid in the Docking Bays; she fought back, but without the Ice Beam, she could not harm the beast. When all seemed lost, the SA-X intervened and attacked the Omega Metroid with its own Ice Beam; as it was still weak from its earlier battle with Samus however, it was quickly overpowered.
This time, Samus was able to absorb the SA-X's Core-X, giving her Fusion Suit one final upgrade. Like the Varia and Gravity Suits before it, this new suit granted Samus additional resistance to damage. It also changed the color scheme of the Fusion Suit to orange-on-yellow, causing it to resemble her old Varia Suit prior to its surgical removal. Finally, the suit restored the Ice Beam again. These effects are the results of Samus literally absorbing herself prior to her infection, surgery, and vaccination.
- When the suit is acquired, Samus does not flash as she does when the Varia and Gravity Suits are retrieved.
- Yoshio Sakamoto has stated that the SA-X restored Samus' original genetic condition and lack of vulnerability to cold temperatures, but not her suit's physical appearance.
- The Suit is not actually named in the game or the code. Through hacking, it has been discovered that the Suit is merely a palette gained as a property of the Ice Beam, but with the added ability to move through liquids freely without the use of the Gravity Suit.
|Samus Aran's Suits|
|Power Suits||Power Suit • Varia Suit (Varia) • Gravity Suit • Zero Suit • Justin Bailey • Phazon Suit • Dark Suit • Light Suit • Fusion Suit • PED Suit • Hazard Shield • "Unnamed Suit" • Fully Powered Suit • Green Samus|
|Attire||Casual Outfit • Military Dress • Civilian Clothes • Parka • Training outfit|
|Mechanics||Power Suit Mechanics • Fusion Suit Mechanics • Zero Suit Mechanics|
|Hybrids||Asborean • Chozo Statue • Darkling • Dark Samus • Dark Suit • Light Suit • PED Suit • Samus Aran • Unnamed Suit|
|Biomechanical||Aurora Unit • Security Robot B.O.X. • Cortex Chamber • Dark Diligence Drone • Dark Ingsmasher • Dark Quad • Fusion Suit • Mother Brain • Nightmare • Quadraxis • SA-X • Space Pirate Boarding Pod|
|Cyborgs|| Crash Pillar • Cyborg Zebesian (Super) • Ghor (-G) • Kyratian • Leviathan Battleship • Pirate Militia • Preed (Dark) • Puffer Mine • Ridley (Meta/Omega) • Samus Aran • Slench • Space Pirate • Weavel • Zebesian |
Large Leviathan-class armed ship • U-ton