OoC: I must agree with @Outis.
Karkat Aims at Riou's head, intent to prevent him from saving Four.
She had to much romance, too much love. He hated love. Hated it with a burning passion. He would have the emotion wiped from the face of the multiverse, eventually. But small steps.
Deal with these folks trying to heal her now, so that she might lose the love as a robot. If she failed to lose her love, he would kill her then.
But that was later, he could get rid of her now, through them.
OoC: @Drak, would you mind if I prevented them from saving her Viva-Karkat?