Kai_Mao on 16 May 2018
I think the inclusion of Eevee as the co-version with Pikachu makes sense.
If you have looked back in recent months, the Pokemon Company and Game Freak have promoted Eevee as a co-mascot to Pikachu. Eevee even got its own giant costume to go along with the giant Pikachu outfit you've seen in promotional material.
https://pokemonblog.com/2018/01/18/first-footage-of-giant-eevee-costume-unveiled-by-the-pokemon-company/
Plus, as someone said, Eevee was the main Pokemon for Blue/Gary in Pokemon Yellow.
