"Ooh, what's this?" asks Brooke's sister, examining the gold ring on her finger. "Is this my sister's? Did you give it to her? It's really pretty."
Your heart nearly stops. "Kira," you plead with her by name as you lift yourself off of her. The realization of what you've just done, having sex with your girlfriend's younger sister, is bad enough. It certainly doesn't need to be complicated by her messing around with the ring. "Take that off and give it back to me. You really shouldn't be wearing that. You don't know what you're doing."
Kira laughs playfully. "Oh, don't be such a buzzkill. My sister and I borrow each other's jewelry all the time. It's really not that big a deal."
"No, it really is," you reply, covering yourself with the bedsheet and trying to keep your shame in check. "Trust me. I... uh... the thing is, I... um... haven't given it to her yet. It's supposed to be a surprise for her. So... uh... could you just give it back and go?" At this point, you're willing to do anything to get the ring back, even if you have to lie.
Unfortunately, you're not very good at lying, and Kira can read your poker face perfectly. "Okay, what aren't you telling me?" she says with a mischievous smirk. "You're hiding something from me. You wanna tell me what it is? Or do I have to tell Sis how much fun we just had?"
You hesitate a moment. Her threat sends shivers up your spine, and you know she'd follow through on it-- but at the same time, you also know it's hollow. The next time you trade off with Brooke, she's going to know what happened anyway, so it's not like you can avoid it. You decide to call her bluff. "Fine, tell her. Just give me back the ring."
"Oh, that is not happening," says Kira, a little surprised by your boldness. She clenches the hand wearing the ring into a fist to make her point. "I'm holding onto this until you tell me what's really going on."
You sigh as you realize there's no other way to convince her to give you the ring. You've got to let her in on your secret, and hope she'll understand how important it is that you get it back. "Alright, alright, fine, I'll tell you everything." Using the bedsheet, you gently wipe the fluids off of your sleeping penis/girlfriend before exposing yourself again to Kira. "Here, look."
She eyes your bare manhood lustily. "Hmm? You want more? What do you want me to do now, suck it?"
"No, no," you say, shaking your head in annoyance. "I just want you to look at it. I mean, really look at it, very closely." Kira shrugs. An odd request, she figures, but she's certainly not going to protest it after the great fuck you and she just had. As she inspects it, she suddenly notices something is off. The skin and hair isn't the right color... and there's something else. "Whoa, wait a minute... you got a tattoo on your dick? When did you do that? Didn't that hurt?" She snickers. "And if you're going to get something there, why would you get a heart?"
"I didn't," you say. "Brooke got the tattoo, on her hip. You asked me where your sister was. Well... here she is."
Kira looks incredulously at your penis once again. "No way..." But she can't deny, the skin and hair color really is her sister's. "You mean... when I was just fucking you... I... had HER inside me?!?"
"Afraid so," you nod. "I didn't want it to happen, but I couldn't stop. She still has a mind of her own, and in the state she's in right now, she was so horny that I literally couldn't resist you..."
Kira's horror turns to fascination as she looks at the flaccid tube of flesh her sister has become. "But... how?? How did she... end up like this?"
"It's that ring on your finger," you explain. "That's why you need to give it back to me. It's magic, half of a pair. Right now she's being affected by the other one. There was a little bit of a glitch, and... well... for the next couple of weeks, the two of us are going to have to keep switching places every so often."
"Switch places?" asks Kira, still wearing the ring. You barely have time to realize how badly you just misspoke before the ring activates. Suddenly...