Dueling Heroes (うずまきカップ！みずのコロシアムでだいバトル！！ Whirl Cup! The Big Battle at the Water Coliseum!!) is the 7th episode of Pokémon: Master Quest.
The Whirl Cup is underway as princess Maya congratulates all the trainers who pass the preliminaries and explains the winner will also get a Mystic Water Pendant. Ash is excited and he swaps Kingler for Bayleef (Which might not make her happy). He goes up against Christopher and his all mighty Kingdra. Can he win using Totodile and who will Misty go up against?
After the preliminary round, the Whirl Cup continues. Before the battles begin, Maya, the water priestess, is going to commence the ritual. Ash and Misty admire her, while Brock is fascinated by her beauty. Maya gives them a speech that welcomes them to the Whirl Cup and announces that every one that has come here respects Water Pokémon. She also tells them they should communicate with the Water Pokémon using the Sea Spirit, a staff she holds. Team Rocket spot it and plan on stealing it, but have to serve the customers first. Maya uses the power of the staff to bless the contestants, then announces the start of the Whirl Cup. The announcer points the winner of the Cup will gain a Mystic Water pendant.
Brock reads the Mystic Water pendant increases the power of attacks of a Water Pokémon. Ash and Misty bicker whose pendant will belong to, but Brock clears the situation and reminds Ash his only Water Pokémon is Totodile. Ash contacts Oak to get Kingler for the Cup. Misty and Brock remind Ash he has to send one Pokémon to the lab, since he already has six. Oak asks Ash to send Bayleef, since he did not have much time studying her. Ash does that, sending Bayleef for Kingler. Oak is pleased and sends Bayleef. Bayleef sees her master is gone and runs around, causing Oak to be tackled. At the tournament, Misty admires the Water Pokémon, who battle. Next contestants are Ash and Christopher. Ash sends Totodile, while Christopher points at the Lure Ball attached to the fishing rod. He tosses the Lure Ball, sending a Kingdra.
Misty and Brock know that Totodile can do well on land and water, but do not know Kingdra's attacks. Totodile dives in the water, but gets pulled by Kingdra's Twister. Totodile is spinned inside the whirlpool caused by Twister and once the Twister stops, Totodile falls down. Kingdra uses Water Gun, but Totodile evades. Kingdra uses Hydro Pump, but Totodile walks on the water stream. Totodile uses Skull Bash, but Kingdra dives in and uses Smokescreen. Totodile comes out, but neither he nor Ash do not know where Kingdra is. Meowth sees that the twerp has a hard time. Jessie is annoyed at him and James for selling the food while they can steal the staff, but happily serves the customers. Totodile yawns at the boredom, but Ash sees they have to stay calm. Kingdra emerges to use Hydro Pump, but Totodile bites its mouth and prevents it. Kingdra gets filled by the water it was meant to use. Once Totodile releases the mouth, Kingdra flies around the stadium spitting water, then falls down in the water, defeated.
Misty and Brock are relieved by Ash's victory. Team Rocket are exhausted, as they always have to sell food instead of stealing the Sea Spirit. Jessie thinks the staff should belong to her, then yells at James and Meowth for advising to sell it. A merchant orders them to work, since they'll get free cotton candy, on which Team Rocket is pleased of. During the night, Misty observes the sea from the house, as she cannot sleep. Ash asks if she is worried, but Misty replies she is excited to be a part of it. Next day, Misty battles a man named Harrison in the Whirl Cup. Harrison sends Qwilfish, while Misty sends Corsola. Qwilfish starts with Water Gun, but Corsola's Mirror Coat reflects the attack back. Qwilfish inhales water to use Pin Missile, at a fast rate.
Team Rocket sneak to get the Sea Spirit. They almost steal it, but Maya moves it. Jenny asks what are they doing here, so Team Rocket tells they came to offer food. Jenny responds that this area is limited only for officials and orders them to walk away. Maya still thanks them, since they offered her food. Corsola uses Spike Cannon against Qwilfish's Pin Missile. The attacks collide, but Corsola is pushed against a wall, while Qwilfish dived to prevent any injuries. Brock thinks Qwilfish has the advantage, as it might be that the best offense is not to use any defensive moves. Qwilfish uses Take Down to hit Corsola, who takes more damage. Corsola heals using Recover, so Qwilfish uses Take Down once more. After the attack, Qwilfish is stuck between Corsola's horns. To finish the battle, Corsola defeats Qwilfish using Spike Cannon.
Misty is pleased with Corsola, who is overjoyed. Ash sees that was close, but Brock thinks Misty's strategy of turning the battle over reminds of Ash's strategy. Meowth sees they lost the opportunity to grab the staff, but Jessie is still determined to steal it. However, Team Rocket still attends the customers. Later, Ash and Misty are pleased to have won. Brock reads the next challengers are chosen by shuffling the previous round's challengers. The heroes go to read the notice board. As fate would have it, they learn they have to battle each other.
The "Who's that Pokémon?" is Aipom.