Ash and Goh have both entered the Vermilion City Pokémon Eating Contest per Professor Cerise's suggestion, with the Professor himself, Chloe, and a very enthusiastic Chrysa watching them in the audience. Ash has chosen to enter with Dragonite, while Goh's choice is his Skwovet. Amongst the contestants are also last year's winner Snorlax and the eating contest legend, Emperor Blaziken. The prize for the winner is a free trip to Unova and all-you-can-eat Unova food. Unbeknownst to Ash and Goh, Team Rocket is also entering, having spent multiple days fasting in order to build up Morpeko's appetite, all in an effort to win the prize and stuff themselves with Unovan gourmet food.
The first round of the contest consists of eating platefuls of Berries. Many Pokémon make use of their natural capabilities to eat them as fast as possible, such as a Hydreigon using all three of its heads and a Bisharp slicing up the Berries. Blaziken and Snorlax hold up easily while less experienced contestants start falling out. Some of the competing Pokémon are small newcomers who avoid seeds in order to avoid filling up too quickly, which is, however, making them slower than the big Pokémon. However, despite being amongst the smaller competitors, both Morpeko and Skwovet perform well. Goh avoids the buildup of seeds in Skwovet's stomach by having it use Bullet Seed into the air, getting rid of the seeds with minimal time loss. As the first round concludes, Ash congratulates Goh while awkwardly admitting that Dragonite turned out to be a surprisingly light eater. The ten Pokémon continuing onto the next round are revealed, including Blaziken, Snorlax, Skwovet, and Morpeko. Having been eliminated from the contest, Ash joins Professor Cerise's group in the audience to cheer for Goh.
The remaining contestants gather in a tent behind the stage. Trying to intimidate Goh, a fellow competitor, a Scientist, reveals that the other remaining competitors are all title holders from big regional tournaments, putting Skwovet and Morpeko at a disadvantage. Before the situation can escalate, Team Rocket arrives to offer cookies to the waiting gluttons. A Lickitung, a Heatmor, a Swalot, and a Vigoroth eagerly accept the offer, but soon Team Rocket's special cookies swell up in their eaters' bellies, making them unable to eat more and eliminating them from the contest.
The remaining six contestants enter the second round, which consists of paired eat-offs, with the winning Pokémon from each pair advancing to the finals. Team Rocket rigs the lottery used to decide the pairs so that leading competitors Blaziken and Snorlax compete against each other, hoping that regardless of which one of them wins, the winner will still be tired out for the finals. The other pairs are Morpeko versus Glalie and Goh's Skwovet pitted against the Scientist's Muk. One competitor from each pair gets to choose their round's dish from a menu: Blaziken's Trainer chooses curry, James chooses Berry pot-au-feu, and Goh chooses Pecha tart. Blaziken and Snorlax eat their curries evenly fast, but in the second pair, while Morpeko isn't bothered by the food's high temperature in the slightest, Glalie, being an Ice Pokémon, has trouble handling the hot food. Glalie's Trainer attempts to solve the situation by having Glalie use Freeze-Dry, only to end up freezing the entire dish inside a block of ice and preventing Glalie from eating it, just as James had planned. In the third pair, Skwovet is downing the tarts rapidly, while Muk is eating very slowly and reluctantly. Goh reveals that he noticed that the Scientist had retreated the moment the cookies had arrived, and quickly deduced that Muk dislikes sweet food. The Scientist confirms this, but also notes that he's trained Muk to stomach any food, no matter its personal tastes. Skwovet, meanwhile, is getting sick of the sweet taste and has stopped eating. Goh had been expecting this, however, and has Skwovet use a Tamato Berry stored in its tail fur to spice up the tart. The spiciness resets Skwovet's taste buds, restoring its appetite. The second round finally ends, with Blaziken, Morpeko, and Skwovet advancing to the finals.
The final round has the contestants eat as much Torchic manjū as they can. As the bell rings, both Morpeko and Skwovet start eating furiously. To everyone's surprise, however, Blaziken hasn't eaten a single bite, not wanting to eat something that looks like its pre-evolved form. As such, after gently wrapping the manjū in a napkin, the legendary glutton leaves the stage. With the strongest competitor out of the way, Team Rocket feels certain of their victory, only to discover, to their horror, that Morpeko has reverted back into its Full Belly Mode, meaning that it has eaten its fill, while Skwovet is still eating. They desperately try to make Morpeko eat more, only for it to attack them with Aura Wheel out of frustration, sending them and itself flying off the stage. Skwovet is now the only competitor left, and is only one tray behind Morpeko's record. However, Skwovet's belly appears swollen and it struggles to eat more. Suddenly, though, Skwovet becomes determined to finish the rest of the food, and, as Goh cheers it on, evolves into Greedent before everyone's eyes. With its now-increased appetite, Greedent easily shoots past Morpeko's record and wins the competition. Goh hugs his newly evolved partner in celebration, preparing for his prize trip to Unova.
Meanwhile, Team Rocket is dismayed by their failure, but as Jessie is about to eat a manjū as comfort food, the trio sees that Morpeko has turned back into its Hangry Mode, its hunger already restored.