You have to win many Link Cable Battles against your friends, get close to completing your Pokedex, and get your Pokemon's pictures painted. I have five fans at the moment however I did have seven. I haven't lost any link cable battles, but yet occasionally one of my fans leaves me and goes back to liking the person they did when you first entered Lilycove City, or they'll like the person I just beat in a Link Cable Battle. I'm not sure why they leave.