At the Kalos League stadium in Lumiose City, Ash is preparing for his World Coronation Series battle against Drasna when Wikstrom unexpectedly enters the room to greet him. He notices that Ash's Farfetch'd has evolved and stops to admire Sirfetch'd for a moment. Drasna then enters the room as well and greets Ash with her partner Pokémon, Altaria. Ash grows nervous around Drasna's presence and shakes her hand. During said handshake, Drasna drops her gentle demeanor and squeezes Ash's hand while, under no uncertain terms, making it clear that she intends to put a stop to his winning streak. Both Ash and Wikstrom are left startled as Drasna leaves the room, musing that she's going to have fun in today's battle.
Both Ash and Drasna enter the battlefield as Clemont, Bonnie, and Goh watch from the audience. Goh notes Drasna's pleasant smile, but Clemont assures him that it's just a facade. Bonnie can attest to that, since her big brother has actually faced Drasna in battle and was utterly defeated by her. Clemont, visibly embarrassed, tells his sister to not remind him of his disgrace. The Drone Rotom gives the signal, and the competitors choose their first Pokémon: Sirfetch'd and Noivern. Drasna makes the first move by ordering a Super Fang, but Sirfetch'd uses its shield to block the attack before striking back with Brutal Swing. Noivern follows up with a Boomburst, which is strong enough to send pieces of the battlefield flying. One of these pieces strikes the shield out of Sirfetch'd's grip, leaving it open for a Dragon Pulse as it tries to retrieve it. The Dragon Pulse also knocks Sirfetch'd's leek sword away, leaving it with nothing to defend itself with as another Boomburst batters the battlefield. The powerful sound waves send pieces of debris and Sirfetch'd's sword and shield flying, so Ash tells Sirfetch'd to use the debris as footing to retrieve its weapons. Sirfetch'd succeeds in this and launches into a Meteor Assault as Noivern starts charging for a Dragon Pulse. In a surprising move, Noivern uses its big wings to block the Meteor Assault before letting the Dragon Pulse loose and making a clean hit.
As Sirfetch'd is unable to move after using Meteor Assault, Ash decides to recall it and send out Dracovish in its place. Noivern goes for a Super Fang, which Dracovish counters with Ice Fang. Both attacks hit their mark, cutting Dracovish's stamina in half and dealing a super effective hit on Noivern, forcing Drasna to make her own recall and send out Altaria. Similar to how it was attracted by Sirfetch'd's leek, Dracovish now gets excited at seeing the swaying plumes on Altaria's head and charges forward without an attack command. While momentarily flustered, Ash decides to go with it and orders an Ice Fang, which, however, ends up being almost completely nullified by Altaria's Cotton Guard. Bonnie notes that Drasna's defensive strategies were also what doomed her big brother's match against her, a fact that Clemont pleads Bonnie not to remind him of.
Drasna decides to unleash her full power and reveals the Key Stone on her wrist. Reacting with Altaria's Altarianite, the Key Stone triggers the Mega Evolution process and turns Altaria into Mega Altaria. Drasna orders a Sky Attack, easily avoiding a Fishious Rend while the attack is charging and then outspeeding an Ice Fang to deal big damage on Dracovish, fully utilizing the increased speed and power provided by Mega Evolution. Altaria follows up with a Play Rough, and Dracovish is too mesmerized by the softness of Altaria's plumage to fight back. As Dracovish is freed from the attack, Ash's eyes focus on Altaria's plumes, giving him an idea. He has Dracovish drench Altaria with a powerful Water Gun, leaving its plumes soaking wet and canceling out an attempted Sky Attack. Seizing the chance, Ash tells Dracovish to attack with a Dragon Rush. Clemont tries to tell Ash to stop, but it's too late, and the attack goes off, only for it to do absolutely nothing. While Altaria shakes itself dry, Drasna reveals that Mega Evolution turns Altaria into a Dragon/Fairy type, meaning that Dragon-type moves are now useless against it.
Following a clash between Breaking Swipe and Ice Fang, which deals damage to both sides, Ash sees that Dracovish is getting tired, so he recalls it and sends Sirfetch'd back out. To everyone's surprise, Dracovish suddenly reemerges from its Poké Ball, eager to cheer for Sirfetch'd. Ash agrees to this and lets Dracovish stay out for moral support. Sirfetch'd meets Altaria's second Breaking Swipe with a Meteor Assault, resulting in an explosion. When the smoke clears, Altaria falls down onto the battlefield and reverts to its regular form, showing that it is unable to battle. However, as Sirfetch'd is being congratulated, it also collapses, likewise unable to continue after spending the last of its power on the Meteor Assault. Wikstrom sheds tears of joy at witnessing Sirfetch'd's chivalrous spirit as Ash recalls his Pokémon, only for it, like Dracovish before, to immediately come back out to cheer for its friend.
Drasna calls out her Noivern, admitting that Ash has pushed her farther than she could have ever anticipated, but now it is time to finish the match. Noivern uses Dragon Pulse, which overpowers Dracovish's Dragon Rush and pushes it back. Keeping up her relentless assault, Drasna orders a Boomburst, which pins the already battered Dracovish to the ground, battlefield debris continuously smashing into the Fossil Pokémon. However, with Ash and Sirfetch'd cheering it on, Dracovish is able to muster its strength and stand back up again. Another collision of Dragon Pulse and Dragon Rush ensues, with both sides giving it their all as a big explosion covers the battlefield. The smoke clears to show Noivern and Dracovish staring each other down, until Noivern collapses. The Drone Rotom rules Noivern unable to battle and declares that Ash has emerged victorious against the Elite Four member. As Ash celebrates his victory and congratulates both of his Pokémon, his ranking is updated, rising from 15 to 9, meaning that he's now at the top of the Ultra Class and only a step away from the Master Class.
Later, Ash and his friends meet up with Drasna and Wikstrom outside the stadium. Drasna congratulates Ash on his performance and warns him that the battles are going to get even harder from this point on. Both she and Wikstrom assure that they'll be cheering for him. Seeing how strong and responsible Drasna is, Bonnie suddenly falls on her knee and asks her to marry her brother. Drasna is left flustered and blushing by this offer, while Clemont, thoroughly embarrassed by his sister's usual antics, picks Bonnie up with his Aipom Arm and drags her away.