In Anistar city theres an old man two houses above the boutique, he asks to take care of a Pokemon under level 5, You can take it back at any time, does this do anything?
He keeps it for company until you beat the elite four. When you come back, you learn that he has passed away, and he left the pokeball with the Pokemon that you lent him inside, a note that thanks you for the Pokemon's company, and a comet shard. Nothing should change about the Pokemon.
Source http://bulbapedia.bulbagarden.net/wiki/Anistar_City#Old_man.27s_house
