>>50671101In Anistar City there's an old man who asks if he can have a young pokemon of yours, just to keep him company because he's been living on his own since his wife passed away.
After you beat Diantha you can go back to the house and the old man has died, leaving you with a kind letter thanking you for giving him some company for his final days, and an inheritance in the form of a comet shard. You also get your pokemon back, which now has max affection. 