The plot could start with Lysandre finding a way to gain control over Ash, perhaps through some new form of technology or a mysterious power. Then Ash is made to do Lysandre's bidding, like stealing Pokémon or sabotaging other trainers. As the story progresses, Ash's friends might notice his strange behavior and start to investigate.
In this fanfic's plot, Lysandre might be after a particular legendary Pokémon. He realizes that Ash has a special bond with Pokémon that could help him get closer to this goal. So, he uses some dark magic or advanced mind - control device to control Ash. Ash is then forced to lead Lysandre to the location of the legendary Pokémon. However, during this journey, Ash's pure heart and the love of his Pokémon start to create glitches in the control. His Pokémon friends, especially Pikachu, try their best to communicate with Ash and break the control. Meanwhile, other characters from the Pokémon world might get involved, either helping Lysandre or trying to save Ash, leading to a complex and exciting plot full of twists and turns.
Well, maybe the plot involves Lysandre having a hidden agenda that requires Ash's unique connection with Pokémon. He controls Ash to infiltrate a powerful Pokémon organization. Ash, while under control, has to fight his own internal battle as his instincts as a good trainer conflict with Lysandre's orders. His friends, such as Pikachu and the others, sense something is wrong and try to break Lysandre's control over Ash. Along the way, there could be battles, both physical and mental, as Ash struggles against the control and tries to expose Lysandre's true motives.