In the Galar region, a young trainer and their best friend Hop receive their first Pokémon from Hop's older brother Leon, the undefeated Champion of the Galar League. Endorsed to take on the Gym Challenge, the two set out across the region, competing against rival challengers and contending with Team Yell, a rowdy group of hooligans devoted to fellow challenger Marnie. Along the way, the trainer encounters Chairman Rose, the powerful head of both the Galar League and the region's primary energy corporation, who seems to have plans that extend beyond the tournament itself.

After a mysterious encounter with an unknown Pokémon in a fog-shrouded forest called the Slumbering Weald, the trainer begins uncovering connections between ancient legends of a catastrophic event known as the Darkest Day and two heroic Pokémon said to have saved the region long ago. As the Gym Challenge reaches its climax and the Champion Cup draws near, Rose's true ambitions threaten to plunge Galar into a crisis that only the trainer and the legendary Pokémon can resolve.