From Bulbapedia, the community-driven Pokémon encyclopedia.
The Grand Harvest Festival (Japanese: Harvest Festival) is a festival that is held on Harvest Island once a year. It was featured in The Journalist from Another Region!.
The Grand Harvest Festival was created after a famine, which started after the locals fought over the rich land and destroyed the island's once-thriving fruit and Berry supply in the process. The two strongest Pokémon on the island, an Ursaring and a Beartic, fought over the last apple, though neither of them decisively won in battle. A local child had watched the melee unfold and split the Berry in half, allowing the two Pokémon to have an equal share. Since that day, the people strove to restore and preserve the land, and the festival was meant to help them celebrate nature. The Berry harvest would attract people from all around the world to help Harvest Island celebrate its folklore.
Several food stalls selling jams and baked goods are also set up to showcase Harvest Island's fresh produce.
A key part of the festival is the Pokémon Sumo Tournament, created to recreate the battle between Ursaring and Beartic. Sixteen Trainers must compete to win a Focus Band and a year's supply of fruit. Ash, Iris, and Cilan all entered, and while Ash took out the victory, in the spirit of the competition, he shared one of his Berries with fellow competitor and runner-up Rodney.