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 completely 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.
In 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.
Calm just like its Trainer, Gardevoir proved powerful in its debut appearance, being able to dodge attacks from opponents with and without verbal commands, also proving a powerful bond with its Trainer.
Diantha uses Gardevoir as her signature Pokémon, saving it for last and Mega Evolving it directly after entering the battle. It is also on her Battle Chateau team after the player defeats the Elite Four.
