I don't think Karkat could do much to Kuja on the psychic level (although I am tempted to have that power affect Genomes slightly differently than typical humans), but emotional...

That has a lot of potential but the first thing to come to mind is Karkat getting in way over his head, since Kuja's a bit of a timebomb when it comes to his own emotions.

Maybe we could aim/plurk about this?