Gardevoir is Diantha's only known Pokémon. It is able to Mega Evolve into Mega Gardevoir.
Gardevoir was first seen fighting against Magnus's Absol, where it used its speed to completely avoid taking any damage before defeating it, doing so without needing to Mega Evolve. Later Gardevoir battled against Pikachu, and was able to complete outmatch its opponent again in terms of speed and power. Before it could win, Gardevoir was captured by Team Rocket who attempted to flee with it. However Diantha followed and Mega Evolved Gardevoir who easily escaped its captors and sent them blasting off.
It was revealed to have evolved from a Ralts in Battling Into the Hall of Fame! and to have been with Diantha since she was young, as it appeared with her on a photo in the Pokémon Summer Camp Hall of Fame.
During Championing a Research Battle!, Diantha used Gardevoir to battle Ash's Greninja. Although Gardevoir initially held the upper hand, it eventually had to Mega Evolve to keep up with Greninja's unique transformation. When Greninja perfected its new form, it overpowered Gardevoir, but passed out from the resulting strain. Gardevoir was then targeted by Team Rocket again, but easily sent them blasting off. It then dropped to its knees in exhaustion, to which Diantha thanked it for a job well done and recalled it.
It then reappeared in A Towering Takeover! to combat Team Flare at Lumiose City.
|A † shows that the move was used recently, unless all moves fit this case or there are fewer than five known moves.