Gardevoir and a greedy Trainer once entered a dungeon where a Ninetales went to put a curse on the Trainer. However, Gardevoir got in the way and absorbed the curse. Ninetales would have undone the curse after seeing how much his Pokémon cared for her Trainer, however, the Trainer ran away and abandoned Gardevoir, leaving her to become an agent of spirits.
Gardevoir first appears to the player in their dreams as a faint voice. This voice eventually gets stronger and Gardevoir eventually reveals herself to the player. She tells the player that she is an agent of the spirits and watches over them. She tells the player that they became a Pokémon to fulfill an important role and once that role ended, they would return to the human world.
After the player gets Rayquaza to destroy the falling star, Gardevoir tells the player that their time as a Pokémon was over and that they were to return to the human world. However, since the partner was heartbroken by this, the player decides to stay and Gardevoir sends them back to the Pokémon world.
After Gengar and the player beat Murky Cave, they rescue Gardevoir and she decides to join the player's rescue team. She has no memory of her past with Gengar following the events in Murky Cave.