Pikachu

Pikachu is Ash's first ever Pokemon and best friend. He has been travelling with Ash over the world for 20 years. He is voiced by Miguel Fernandez.

Appearances
The Milf, the Mime and the Maniac

For a God's Sake

Rocket 'n' Rotom

Time Flies

Shorts
Why Serena isn't in Alola

Ash trains with Rockruff

Serena cuts her hair

Other
Ash Ketchup Vs. Serena

Ash Ketchup Vs. Dawn

Ash Ketchup Vs. May

Trivia

 * Pikachu is voiced by Miguel Fernandez, who along with Anthony Fernandez, writes and directs most episodes and voices multiple characters.
 * Pikachu is known to have a history of manslaughter and borderline sexual assault... as seen in "Rocket 'n' Rotom" where he apparently killed Mimikyu and somewhat forced Buizel into a sexual situation as seen in "Ash Ketchup Vs. Dawn"... both events pre-series (Sun and Moon Abridged).