How can Urumin favour her number one fan too much? She only has one fan (counting those that anyone would be aware of), so technically all of her attention goes to that single fan, no matter what she does. Favouring one over the others requires there to be others. For Urumin, they don't exist. Telling Urumin not to cause trouble is a different thing, though. It would also be a problem if the numerous fans of the other idols in the group start to expect as much attention as Kimiya receives from Urumin. That would be impossible since the others have more fans. There's only so much attention they can be given.