We learn more about James past and his home life before he joined Team Rocket. James leaves his Chimecho at his Summer Mansion so it can recover and he gets a Mime Jr.
James starts to cry before telling his grandparents that he'll leave it behind. James then gets Chimecho's PokeBall out but several falml out and one even enlarges. Seeing the enlarged PokeBall. Mime Jr runs over to it and taps the button and Mime Jr is bought into the ball. James waves to his Chimecho as he departs off into the sky.
So sad yet, it was so sweet. :)