In Pokémon: Indigo League, Ash receives Pikachu from Professor Oak.
Ash arrives late at Professor Oak’s laboratory and finds that the three traditional starter Pokémon—Bulbasaur, Charmander, and Squirtle—have already been chosen. Oak gives him Pikachu instead, beginning the partnership that defines the animated series.
At first, Pikachu refuses to stay inside its Poké Ball and does not readily obey Ash. Their relationship changes after Ash risks himself to protect Pikachu from a flock of wild Spearow. That early episode establishes the trust that becomes central to their journey.
The game protagonists normally choose from Bulbasaur, Charmander, or Squirtle, so viewers sometimes confuse Ash’s anime origin with the game opening. Pikachu’s role also connects the anime to Pokémon Yellow, whose design was influenced by the television series.