Niantic has been launching regular updates for Pokémon GO since its release back in July, and the next update (which is reportedly available to some users already, but hasn’t launched in most areas) adds in the rumored Buddy Pokémon feature. Designating one of your Pokémon as your Buddy will make them appear alongside your avatar on your profile screen, and you’ll rack up candies just by walking together.
If you choose Pikachu as your Buddy Pokémon, you can enjoy a fun reference to the Pokémon anime. Pikachu initially disliked Ash, but the two eventually grew so close that Pikachu is frequently seen riding on Ash’s shoulder. This is reflected in Pokémon GO, as walking 10 kilometers with Pikachu as your Buddy will lead to him hopping up on your shoulder when viewing your trainer details.
Source: The Silph Road