Pokémon the Movie: I Choose You!(劇場版 ポケットモンスター　キミにきめた！)

This is the story of how Ash and Pikachu first met. At first, Pikachu was disobedient towards Ash, but Ash only wanted to be friends with Pikachu. On the day they set out from Pallet Town, both of them saw a Ho-Oh flying and they made a vow to meet it.