Could Friede's Pikachu be the one that currently belongs to Ash? Here's how it could be:
The Pokemon G-men, led by Lance, were building up a case on Ash all throughout his journey. They developed an interest in him because he flouted the Pokemon league rules on numerous occasions to obtain badges illegally, in addition to using illegal moves and abilities to gain an unfair advantage. His first crimes were committed in Kanto, where he threw rocks at Pokemon to capture them, sadistically sent out his Caterpie vs Pidgeotto in hope that he would see it get eaten and falsely imprisoned Pikachu by tying it up and dragging it against its will. Then he doped Pikachu up after losing to Brock and took advantage of the broken sprinkler system to beat Brock when he showed mercy on him. He built a bond with Misty to obtain the cascade badge without having to beat her in a battle, and had his Haunter commit an act of terrorism to force Sabrina to give him a badge when he knew he couldn't win vs her. After that, he was willing to win the Volcano badge at all costs, even if it meant Pikachu getting cooked in lava. Pikachu was also hacked to be able to use moves that shouldn't ordinarily work on ground types.
This is just his Kanto crimes. Don't get me started on the other regions...Maybe Friede gets custody of Pikachu after Ash gets arrested. I did say before that a rainbow is a bad omen.