Katherine caves

"Uhhmmm," you hear to the side. Katherine is starting to move again, trying to get you attention. You draw your cock out of Sabrina's vice-like asshole and let Sabrina collapse onto the pillows underneath her.

You move over to Katherine and tell her, "If you're ready to listen to me, nod your head."

Katherine nods her head.

"You must do exactly as I say, exactly when I tell you do, and without argument. Do you understand?"

Katherine nods her head.

"If you do not follow my directions exactly, or I catch you trying to undermine me, I will punish both you and your sister. Do you understand?"

Katherine nods her head again.

"Good," you say, "Now to prove you'll do exactly what I tell you, you're going to use a strap-on I purchased to complete Sabrina's punishment that you've caused. That means you're going to fuck her asshole with it, do you understand?"

Katherine pauses and then nods helplessly. You hear Sabrina behind you trying to plead but all that comes out are muffled noises.

You slip the strap-on onto Katherine - its not gigantic, but certainly big enough you aren't even sure if it will fit in Sabrina's unused behind.