All of Wyndon Stadium waits with anticipation as the fourth and final match of the World Coronation Series Masters Eight Tournament quarterfinals, featuring Hoenn Champion Steven and Ash, the first Champion of Alola, prepares to begin. In the audience, Team Rocket, still broadcasting the events of the tournament, are excited to see Ash battle, though Jessie believes Ash has no chance of victory against Steven. Meanwhile, Goh has Hop move over so that Iris, having desired to feel the excitement of the stadium in person like Ash had for the previous battles, can join them in the bleachers. Hop is shocked to meet the Unova Champion in person, while Iris is excited to meet Leon's younger brother and affectionately cuddles up to his Wooloo.
Dan recites the rules once more: the matches in the first round are three-on-three battles with no restrictions on time or exchanges. In addition, each Trainer is allowed only one use of either Dynamax, Z-Moves, or Mega Evolution. Hop is surprised to see that Ash has the ability to use all three. Ash declares to Steven that he will be the one to advance to the semifinals. Steven, eyeing Ash's Dynamax Band, Z-Power Ring, and Mega Glove, notes Ash's confidence despite the status and strength of the former. On the count of three, both Trainers call out their first Pokémon. Steven chooses to lead with his ace, his Shiny Metagross, while Ash selects Dracovish. Backstage, Leon looks forward to seeing what Ash, the "rookie Champion", has to show.
At Dan's signal, the battle begins. Ash calls for Water Gun, but Metagross uses Agility to dodge and move in close. Ash then calls for Fishious Rend while Steven orders a Psychic. Fishious Rend manages to subdue Psychic and cause Metagross damage, but Dracovish is still sent flying back by the attack. Steven mutters that Ash predicted his strategy. In the audience, Goh notes that Fishious Rend's power increases if the attack goes first, while Iris adds that the move is boosted further by Dracovish's Ability, Strong Jaw. Internally, Ash thanks Paul for showing him Metagross's strategy of approaching with Agility and then attacking with Psychic. Seeing the damage Dracovish's attack caused, Steven chooses to recall Metagross in favor of Aggron. Steven notes that while he is the strongest Trainer in Hoenn, that alone is not enough for him, adding that he entered the World Coronation Series to become the world's strongest Trainer. Backstage, Diantha notes that she has never seen Steven so fired up before. Ash responds that it is the same for him, and that he will win the tournament for every person and Pokémon who has cheered them on to this point. Ash calls for Dragon Rush, but Aggron's Heavy Slam overpowers the attack and flings Dracovish back. Though Dracovish gets back on its feet and seems able to continue, it suddenly collapses and is ruled unable to battle by Dan. Iris is sad that Dracovish lost, while Ash recalls and thanks it for its effort. For his second Pokémon, he selects Gengar, who immediately uses Will-O-Wisp to burn Aggron, causing it to stumble. Undeterred, Steven has Aggron use Smart Strike, which sends Gengar flying, but Aggron's burn saps more of its strength. Aggron uses Rock Tomb in an attempt to trap Gengar, but the latter uses Dazzling Gleam to easily free itself and hit Aggron. Once again Aggron takes damage from its burn and collapses to the ground, unable to continue battling. At Professor Oak's Laboratory, all of Ash's Pokémon, especially his Fire types, cheer in happiness.
Steven recalls and thanks Aggron, then sends out Cradily as his third Pokémon. Cradily uses Power Whip, surrounding Gengar with its many tentacles and striking it multiple times. The tentacles then wrap around Gengar, who struggles to break free. Steven then calls for Ingrain, which Alain notes will prevent Cradily from being recalled. Diantha takes this as a sign that Steven intends to defeat Gengar here and now. Ash orders a Sludge Bomb, which scores a direct hit; however, Ingrain slowly begins restoring Cradily's health. Steven then calls for Meteor Beam, the attack's intense light blinding Ash and Gengar. Ash realizes he can fight light with light and shouts for Gengar to use Dazzling Gleam, which blocks Meteor Beam and results in a massive explosion that damages both Pokémon, but also frees Gengar. Steven compliments Ash's strategy, the two Trainers calling for Power Whip and Shadow Ball, respectively. Gengar avoids several tentacles and launches its attack, but Cradily bats it aside and batters Gengar with its attack, flinging it into the ground and defeating it. Recalling Gengar, Ash selects Pikachu, whom Steven calls Ash's greatest partner, for his final Pokémon. Knowing that Electric-type attacks are not very effective against Grass types and Cradily is still restoring health with Ingrain, plus Metagross waiting in the wings, Goh and Hop note that Ash needs to finish Cradily quickly. James and Meowth are excited to see Pikachu, and now Jessie is cheering for Ash as well, telling Pikachu to not lose. Steven orders Cradily to use Rock Blast, but Pikachu's Quick Attack strikes first. Pikachu then leaps from one rock to another to gain height and wraps up Cradily's Power Whip with Electroweb, a manuever that leaves Leon impressed. With Cradily's tentacles out of the way, Pikachu lands a super effective Iron Tail, taking Cradily out of the fight and leaving both sides with only one Pokémon left. Steven praises Ash's skill, remarking that every attack that the latter launches leave him surprised. Ash credits Gengar's efforts in assisting with Pikachu's victory.
Steven recalls Cradily and sends out Metagross once more. Immediately he grasps his Mega Stickpin and Mega Evolves Metagross. Ash calls for Thunderbolt, but Metagross effortlessly avoids the attack, as well as several follow-up Thunderbolts. Metagross uses Meteor Mash, which smashes into Pikachu and causes big damage. Diantha notes that Mega Metagross is said to have far superior strategic and information process capabilities than its base form, enabling it to predict Pikachu's every action with incredible accuracy. Ash calls for Iron Tail, but Metagross easily dodges again and smashes Pikachu into the ground with Psychic, though Pikachu is still able to stand back up. Ash's grimace gives way to a smile as he tosses his hat to Pikachu and the two begin to perform their Z-Move, much to the excitement of the audience. Pikachu fires 10,000,000 Volt Thunderbolt, but Metagross dodges and prepares to finish Pikachu with Flash Cannon. To Steven's shock, however, the lightning bolts suddenly change direction and block Metagross's attack, as well as strike the Iron Leg Pokémon and send it plummeting to the ground. While Steven is in disbelief of Pikachu's ability to command electricity, Pikachu strikes Metagross with Iron Tail, scoring the finishing blow on his opponent. Dan rules Metagross unable to battle and Ash the victor. With that, Ash advances to the semifinals to battle Cynthia, who is excited at the prospect. In the audience, Goh and Iris dance with Grookey in celebration while Hop calls Ash and his Pokémon incredible. Team Rocket is likewise thrilled with the upset, Jessie even believing that Ash might win the entire tournament. Steven congratulates Ash, attributing the victory to the feelings Ash and his partners have for each other coming together to form an incredible power. With the battle over, the four Trainers advancing to the semifinals have been decided: Leon, Diantha, Cynthia, and Ash.
Outside the stadium, Steven expresses his belief in Ash's ability to defeat Cynthia. Alain and Iris likewise tell Ash to win, which he promises to do. Ash says goodbye to the three, while inside the stadium, Leon looks down upon the battlefield impassively.
