The last Lysander sees of his little sister, she's floating away on a Drifloon. He runs after her and jumps, but he can't jump high enough. He yells at her to let go, to fall but that just makes her eyes squeeze shut tighter.
She's afraid of heights.
He wonders if he had been old enough to have a Pokémon, if he could have fought it off. Zapped it out of the sky (nono, not at the risk of her). Maybe flown after her on a bird, and caught her.
When he gets his first Pokémon, it's one that chooses him. A Phantump that comes to his home. Part of him wants to believe that it's his sister. The other part is terrified of what that would mean. It doesn't help that the Pokémon is female.
Ultimately, he takes it as a sign.
They are going to change the world together.
She helps him catch other Pokémon. She follows him in battle and outside of it. He wants to make the world a better place for her. For them.
Something worries him.
For her to reach her full potential, one day he will have to trade her. And he will have to trust that she will be traded back to him.
A few years in, he thinks he's found someone he trusts. So he agrees to trade.
Something in him breaks when the trader takes her and runs.
He had known she was different, but he had always thought that it was because she was his sister.
Humanity is cruel, and that day he vows he will make it better. For her.
He will get her back, and together they create something beautiful.
( One day he does get her back, but by then, the dream has grown far beyond them, into something terrifying. He doesn't notice, too enraptured by it )
Use of Pokémon lore can make things take a scary turn. Happy Halloween