Pikachu hadn't always been afraid of Poke Balls, once he had thought
that they were interesting since they could catch pokemon.
He remembered why he was afraid of them and quite easily, he still
got nightmares because of that day.
He had been walking in the forest one night when a gang of human
teenagers spotted him, they then proceded to throw large rocks at him. The
nect thing he knew they were throwing pokeballs at him, not to catch him
but to hit him.
They did this till Pikachu was hurt too badly to move, and then they
had walked away. He had lay there too hurt too move and he knew that he
was dying, then the human professor Oak had come. Oak had saved his life
but it came with a price, he was in one of the now dreaded pokeballs.
The only good thing about that experience was that he got Ash out of
the deal, now all he had to do was figure out how to train the human.
Humans were always hard to train, but they were good pets and could
transport your friends about.