Ash Ketchum wakes up late one morning after having tossed his alarm clock in his sleep. He makes it to Professor Oak’s lab, but is told that the three starter Pokémon (Bulbasaur, Squirtle and Charmander) have already been taken by trainers who were on time. However, Oak reveals that he has one more Pokémon, an electric type named Pikachu. Despite its volatile and feisty personality, as well as its refusal to get inside a Pokéball, Ash happily takes the Pikachu for his journey.
Outside of Pallet Town, Ash encounters a Pidgey. When Pikachu refuses to fight it, Ash tosses a rock at it, but it hits a Spearow that mistakes Pikachu as the culprit. Soon, more Spearow show up forcing Ash and Pikachu to run. Injured and tired, Ash tells Pikachu to get inside its ball, but it once again refuses. Instead, Pikachu defends Ash from the Spearow by summoning a large thunderbolt that scares them away. As the storm ceases, a Ho-oh flies above and drops a feather called the Rainbow Wing. Ash and Pikachu decide to go meet the legendary Pokémon.
During their travels, Ash catches a Caterpie and the group eventually settle at a Pokémon Center. A trainer bursts in claiming that it encountered an Entei, a legendary fire Pokémon, causing Ash, as well as several other trainers, to rush into the woods to look for it. Ash finds the Entei, but ends up fighting over it with a trainer with a Piplup named Verity. They are also joined by an aspiring professor named Sorrel who uses a Lucario to fight. When Entei escapes, Ash and Verity get into an argument and Sorrel leaves, telling them that they need to find shelter soon. As Ash and Verity fight, they accidentally disturb an Onix that starts chasing them. They manage to get it to leave just as it begins to rain. As they look to find shelter, they find a Charmander that has been left out. They quickly learn that it belongs to a ruthless trainer named Cross who, along with his Lycanroc, left it out in the rain. He carelessly refuses to take it back, calling it weak, and Ash and Verity are forced to find it shelter.
They come across a cave where Sorrel and Lucario just so happen to be and help Charmander back to health. Entei and several other Pokémon arrive to sleep for the night and Ash reveals the rainbow wing. Sorrel reveals that the Ho-oh only gives the wing to the “rainbow hero” who is destined to fight it, as a shadow Pokémon named Marshadow watches. The next morning, Ash convinces Charmander to join them. The group venture on with Caterpie evolving into a Metapod and Charmander evolving into Charmeleon. Sorrel studies more about Ho-oh and the legendary Pokémon while Verity spots Suicune. Eventually, while battling other trainers in town, Cross returns and challenges Ash’s Charmeleon with his Incineroar. Charmeleon is savagely defeated, causing Ash much grief.