What if Pikachu WASN’T Ash’s partner?

that would have changed the whole story I mean pikachu was the reason the original trio formed without that ash probably would go through his journeys solo

It would be treecko

If Ash had woken up on time, there was no guarantee that he would have had one of the Kanto starters. While we, the player, have first pick in the games, there was no reason for the Anime to follow suit by having Ash get first pick. This means Ash could have been the last one to pick and consequently get Pikachu, yielding the Trainer/Pokémon duo we have known for the past 25 years. Yet the one thing I wished the Anime would have answered in those 25 years Ash was our protagonist was who the other Kanto trainers were that took Bulbasaur and Charmander. We know Squirtle went to Gary given he had Blastoise but we never found out about the other two trainers who took Charmander and Bulbasaur respectively. The fact Gary also had an Eevee was the Anime's not so subtle nod to Pokémon Yellow.

Yet if Pikachu wasn't Ash's partner, I'm honestly not sure what Pokémon would have worked. Pikachu was a good partner choice because it requires a Thunder Stone to evolve. Meaning if they wanted to keep Pikachu indefinitely, all it required was Ash never using a Thunder Stone and they broached that subject early when he faced Lt.Surge. Made the decision never to evolve it because that's what Pikachu wanted. Eevee could have worked in that regard initially with the Kanto variants but once they introduced the Johto Eevolutions, it would have been hard to keep Eevee as is. Ditto when the Sinnoh and especially Kalos Eevolutions were introduced. Not going to lie, I would have loved Ash with an Eevolution and specifically Sylveon given the bond Ash would have had with Eevee at that point.