At the end of Metroid II: Return of Samus, Samus Aran encountered a Metroid Egg, the last of the species after she exterminated them, and it hatched in front of her, producing a baby. She spared it after being unable to bring herself to kill it, and took it with her, bringing it to the Space Science Academy to study. The Lab Workers research it and discover that its energy-draining abilities can be used in reverse, to restore energy, thus possibly helping them to save the galaxy from its energy crisis.