No sooner have Ash and Goh arrived at Wyndon Stadium for the long-awaited World Coronation Series Masters Tournament that a boy runs up to them and demands a battle with Ash, despite being fully aware of his status as a member of the Master Class. Not one to turn down a challenge, Ash immediately accepts, but the match ends up being short-lived, as Pikachu defeats the boy's Wooloo with a single Iron Tail. To Ash and Goh's surprise, the boy reveals that he's Leon's younger brother, Hop. Having sworn to be the one to defeat his big brother, Hop challenged Ash to test out the strength of the person his elder sibling is always talking about. Hearing that Leon talks about him makes Ash super excited. Nearby, Team Rocket is hosting a live stream of their radio show to cover the tournament, although their main goal is to scout out strong Pokémon for them to steal.
After reuniting with Iris on his way to the locker room and the rest of the Master Class in said room, Ash joins them for the opening ceremony. One by one, the announcer introduces the Masters Eight to the audience: Ash, the first Champion of Alola; Iris, the aspiring Dragon Master and young Champion of Unova; Alain, a Mega Stone excavator and the winner of the Lumiose Conference; Diantha, the world-famous actress and Champion of Kalos; Lance, a member of the Pokémon G-Men and the newly crowned Champion of Kanto and Johto; Steven Stone, the heir of the Devon Corporation and the Champion of Hoenn; Cynthia, the world's renowned authority in Pokémon archeology and the Champion of Sinnoh; and finally Leon, the undefeated Galar Champion and the reigning Monarch. Leon invites all the other competitors to face him with their full strength, declaring he and his team will battle anyone and emerge victorious. With the introductions done, the matchups of the first round are selected via random shuffle. In the first battle, Leon will battle Alain; the second match will have Lance and Diantha facing each other; Cynthia will face Iris in the third match, much to the latter's worry; and Steven is pitted against Ash for the fourth match. Steven expresses positivity at the chance to finally have a battle against Ash. While the other Champions return to the locker room to wait for their respective turns, Ash joins Goh and Hop in the stands to experience the atmosphere of the battle first-hand. When questioned by Cynthia why she doesn't join them, Iris reveals her hopes to take a picture with her and Diantha, a request both women are fully happy to oblige. Lance and Steven discuss the latter's familiarity with Alain. Though Steven acknowledges that Alain is a powerful Trainer, facing Leon in the first round could be overwhelming for him.
Leon and Alain enter the battlefield to begin their match. Dan recites the rules: the matches in the first round will be three-on-three with no restrictions on time or exchanges. In addition, each Trainer is allowed only one use of either Dynamax, Z-Moves, or Mega Evolution. At his signal, the two Trainers send out their first Pokémon, with Alain leading with Chesnaught and Leon choosing Rillaboom, making the first match-up a clash between Grass types. Alain makes the first move with Hammer Arm, which Rillaboom defends against successfully. Leon surprises everyone by going for his Gigantamax right off the bat, summoning Gigantamax Rillaboom onto the battlefield. His first attack comes in the form of a G-Max Drum Solo. While the G-Max Move is able to partially penetrate Chesnaught's Spiky Shield, the Spiny Armor Pokémon still withstands it, just like Alain had planned. Rillaboom next attacks with Max Airstream, which Chesnaught rides with Gyro Ball. Chesnaught manages to land the attack on its foe, though backstage, Diantha notes that Rillaboom's Speed has now increased as a result of Max Airstream. After blocking Chesnaught's Pin Missile with Max Quake, Rillaboom reverts to its normal form and proceeds to use its Speed increase to outmaneuver Chesnaught's second Gyro Ball and defeat it with Acrobatics, giving Leon the first knockout. Steven and Lance note that Leon was one step ahead of Alain in the Grass-type showdown, signaled by Rillaboom's knowledge of Acrobatics.
Alain's next choice is his Charizard, drawing the excitement of Ash, who reveals to Goh and Hop that he has battled Alain's Charizard many times in the past. Noticing the fire in Charizard's eyes, Leon is eager to test the strength of his next opponent. Charizard easily powers through Rillaboom's Drum Beating with Flare Blitz and deals a super effective hit, taking Rillaboom out and evening the odds. Leon responds by sending out his own Charizard. However, after Dragon Claw is dodged and his Charizard takes a hit from Air Slash, Alain figures he can't get close enough and recalls Charizard in favor of Malamar, hoping to use it to turn things around. This hope is soon crushed, however, as Malamar's Psycho Cut is blocked by a Fire Blast, and the Overturning Pokémon's attempt to use Throat Chop ends with it being grabbed and taken down by a close-range Fire Blast, leaving Alain with just his Charizard, which rejoins the battle while Leon announces that he will keep his own Charizard out. Alain declares that it's his goal to surpass Leon's Charizard and uses his Mega Ring to Mega Evolve his partner into Mega Charizard X, much to Ash's thrill. Alain's Charizard powers through its opponent's Ancient Power with Dragon Claw and deals a successful hit, but its subsequent Flare Blitz results in it getting struck by a point-blank super effective Dragon Pulse, defeating it and eliminating Alain from the tournament.
With Leon moving on to the semifinals, the first battle of the first round of the Masters Tournament has come to a close. Alain accepts his loss and swears to redo his training in preparation for a rematch. To decide Leon's next opponent, Lance and Diantha leave the locker room and step out onto the battlefield, preparing to start their own battle.