Pikachu

Pikachu (Japanese: ピカチュウ Pikachu) is an Electric-type Pokémon introduced in Generation I. It evolves from Pichu when leveled up with high friendship and evolves into Raichu when exposed to a Thunder Stone. In Alola, Pikachu will evolve into Alolan Raichu when exposed to a Thunder Stone. Pikachu has a Gigantamax form. Pikachu with the Gigantamax Factor cannot evolve. In Pokémon Yellow, the starter Pikachu will refuse to evolve into Raichu unless it is traded and evolved on another save file. Pikachu is popularly known as the mascot of the Pokémon franchise and one of Nintendo's major mascots. It is also the game mascot and starter Pokémon of Pokémon Yellow and Pokémon: Let's Go, Pikachu!. It has made numerous appearances on the boxes of spin-off titles. Pikachu is also the starter Pokémon in Pokémon Rumble Blast and Pokémon Rumble World.

Ash Ketchum
Ash has a Pikachu that he obtained from Professor Oak in Pokémon - I Choose You!, the first episode of the Pokémon anime, which also marked its debut. He is the signature Pokémon of the anime series and has appeared in every non-special episode, with the exception of Time After Time!, and also every Pokémon movie since. In The Climb to Be the Very Best!, he was revealed to be capable of Gigantamaxing. Ash's Pikachu always remains outside of his Poké Ball.