Pikachu is the player’s partner from the beginning of Pokémon Yellow.
Released in Japan in 1998, Pokémon Yellow is an enhanced version of the first-generation Game Boy games. It was designed to reflect elements of the Pokémon anime, including making Pikachu the player’s initial partner rather than offering a choice among Bulbasaur, Charmander, and Squirtle.
Pikachu follows the player outside its Poké Ball and can refuse to evolve with a Thunder Stone. The game also gives the player opportunities to obtain Bulbasaur, Charmander, and Squirtle during the adventure, so Pikachu is not the only first-generation starter available.
Pokémon Yellow helped reinforce Pikachu’s role as the franchise mascot. Its anime-inspired presentation distinguished it from Red, Green, and Blue while retaining the same broad Kanto adventure.