Diantha arrived to the café and stopped Lysandre from intimidating the children. Diantha was displeased about Lysandre, who intimidated the children, hardly considering that an act of beauty and Mega Evolved her Gardevoir to protect the children.
Diantha had Gardevoir use Psychic to stop Skrelp from attacking and lifting Gurkinn out of the water. Diantha then faced Chalmers and had Mega Evolved her Gardevoir, who used Psyshock to counter Dragalge's Sludge Bomb. Due to its new ability, Pixilate, Mega Gardevoir fired Hyper Beam, which turned into a fairy-type move, which defeated Dragalge. Facing a thief, Diantha sent Gardevoir to battle the thief's Binacle, along with Gurkinn's Heracross and Korrina's Lucario. Since they were facing Binacle, who used two of their heads at once, Diantha Mega Evolved her Gardevoir.
Dinatha, along with Korrina and Gurkinn, arrived to protect the Xerneas tree. Diantha Mega Evolved Gardevoir, who started attacking. Malva appeared and challenged Diantha, having her Braixen trap Diantha and Mega Gardevoir inside the Magic Room Malva was surprised Magic Room did not negate the effects of the Mega Stone. Nevertheless, Braixen used Fire Spin, which Mega Gardevoir dodged. Malva expressed her real intention is to trap Diantha inside, as Diantha, Malva and her Pokémon were trapped into a sphere, which sank into the ground itself.
Seeing Y's progress during his training, Gurkinn had thought of Korrina, Diantha and her Gardevoir, wondering if they would approve if he gave Y the Key Stone. While going underground with his Rhyperior, Blue found Diantha, Gardevoir and Pumpkaboo underground, since Diantha Diantha had been defeated by Malva.
Diantha and Gardevoir set off with the group to the Pokémon Village. Diantha opened her Poké Ball with her heel and sent Gardevoir out, who protected Diantha from Malva's Talonflame's attack. However, Malva obtained Diantha's Key Stone and flew off with her Talonflame; Diantha had her Gardevoir lift them in air to chase Malva. Y's Fletchy fired an attack on Malva and Talonflame, causing the former to drop the Key Stone. Diantha asked Y to step out of the fight, as she, as a Champion, would settle the fight against Malva. Diantha's Gardevoir fired Charge Beam against Talonflame's Razor Wind. Malva, however, intensified her attacks, as Talonflame used Acrobatics, which nearly made Diantha fall down, as she was saved by Gardevoir. Malva and Talonflame dodged Gardevoir's attack, while Malva continued to taunt Diantha. Seeing Lysandre was falling down from Zygarde, Malva dived down to rescue him. Gardevoir fired an attack, which defeated Talonflame.