Oh my god oh my gooood that sounds amazing :o
I think Karkat would work better as a werewolf than a vampire so this works out pretty well!

I think maybe Nepeta could try to kill him but then falls in love with him?
Or maybe them be friends or something and then he turns into a werewolf and /then/ she has to hunt him?
....This could become many things xD

On a side note, who's going to do bonus round 2?