She makes you clean her up

As you lay on Gwen's bed, you feel you feel her seed leaking out of you, and before you could react, you suddenly felt the familiar glass plug press into your ass. This time your asshole swallowed it eagerly, sealing your sister's cum inside you.

"Can't have you leaking all over my bed" she said smiling as she took off your gag.

"You're.... such a sadistic bitch..." you said panting.

"Next time you'll think twice about cuffing me" she said. Also you have one last task: clean me up. She presented her semi-flaccid cock to you.

"What?" you ask

"My cock is covered in cum and juices from punishing you. So it's your responsibility to clean it up."

"And what makes you think I'll do it?"

"It's part of your punishment, so if you don't do it, I won't take off your handcuffs."

"...You're such a sadistic bitch" you repeated. Given everything Gwen has done so far you didn't doubt that she would keep you handcuffed as long as she wanted, in fact that might be preferred for her. You feel Gwen's hot cum swirl inside you as you position yourself to be face to face with her cock. You give it a tentative lick and are immensely relieved that all you taste is cum and sweat, but in hindsight it makes sense. You haven't eaten anything since transforming into a girl, so the only thing that's been through your intestines is Gwen's cum. You run your tongue back and forth along the shaft, trying to ignore how it's hardening as you lick up the remains of yours and hers cum, but no matter how much licking you do, there's always seems to be a little precum left at the tip. Eventually you take the whole shaft into your mouth to give it a proper clean, bobbing eagerly up and down while trying to ignore your own fresh arousal. Eventually you feel the shaft spasming in your mouth.

"Hnnng.." Gwen grunts as she cums directly into your mouth. Your cheeks puff out slightly, but you manage to swallow the whole load without spilling any.

Gwen admires her now completely clean shaft "Well done sis. That deserves a reward." Gwen's praise makes you feel surprisingly warm as you feel her fingers enter your cunt and curl up into your g-spot. She kisses you deeply, her tongue mingling with yours as she fingers you to a short but intense orgasm.

"Good girl" she says as she unlocks the handcuffs.