Of the hundreds of Pokemon to appear in the Pokemon anime over its 19 season run, none is more popular than Ash's Pikachu, the face of the entire Pokemon franchise. For nearly twenty years, Pikachu and Ash have done everything together: winning Gym Badges, exploring strange new Regions, and sending Team Rocket blasting off thousands of times. But what if Ash wasn't Pikachu's first trainer?
Recently, AnimeBlog posted a year old fan theory from the Reddit user Ourfour that posits that Pikachu was actually bred in the Sinnoh region and had another trainer prior to arriving in Kanto. Since Pikachu's Poke Ball has a electric bolt seal on it, a feature only found in Pokemon Diamond, Pokemon Pearl and Pokemon Platinum, he must have came from the Sinnoh region featured in those games. The theory also points out that Pichu (Pikachu's pre-evolved form) only evolve when they have "high friendship", so Pikachu must have been close to another trainer before meeting Ash.
Ourfour's theory is that Pikachu was bred as a backup generator (similar to the "Pikachu Generator" seen in the second epsiode anime) for Professor Oak and was disobedient to Ash because he missed his previous trainer. That seems a little cruel, but we've seen plenty of questionable stuff in the Pokemon anime over the years and no one has ever batted an eye. If true, it certainly explains why Ash has a history of adopting other people's Pokemon as his own. Ash's Charmander, Froakie, Tepig and Buizel also belonged to another trainer before meeting Ash, and each became valued members of his team.
Of course, the biggest flaw in Ourfour's theory is that neither the Sinnoh region or Pichus were part of the Pokemon mythology when the Pokemon anime debuted in Japan in 1997, and the anime often deviates from the game, especially when it comes to certain types of evolutions. Still, it's a pretty cool theory to think that Pikachu has a "secret origin" still waiting to be explored.