Call the girlfriend over.

"No more right now," you tell the pleading girl on her knees in front of you. "We'll do plenty soon enough, and not just blowjobs."

"Oh, that sounds great! I'll do anything you want!"

You pull your pants up and smile. "I'm sure you will. But tell me a little more about your girlfriend."

"Well, she's a goth, like me. She died her hair all black, except for some red steaks. Her hair goes all the way down to her ass, so it really looks hot. She's pretty short, like I'm only five three, but she's not even five feet. Oh, and she has D-cups and a tiny waist, so she has a better figure than me, or she did before you gave me these." Katie shakes her big tits again, showing off how the large mass can really sway back and forth.

"She sounds hot! Call her and tell her to come over here. Make up some excuse, just get her here."

Katie reaches over to the purse she dropped by the floor and pulls out a tiny black cell phone. After a couple minutes of pleading (and a hasty excuse for why she's calling her 'Shelly' instead of 'Raven') Katie convinces her girlfriend to come over. You give her some instructions on what to do when the other girl arrives, then have her make you a sandwich while you wait.

Half an hour later, there's a knock on the door. You have Katie answer it. The tiny goth girl on the other side is just as cute as your slut promised she'd be. She's dressed in black, of course. Her skirt is a lot longer than Katie's, but it and her vest are so tight that they show off all her great curves.

Shelly's eyes go straight to Katie's breasts. "What the hell happened to you!"

"I know, isn't it great!" says Katie as she waves her girlfriend inside and shuts the door. "I've been planning this for weeks and I wanted to surprise you!" The two girls sit on your couch while you wave hello from an armchair.

Katie doesn't give the other girl time to think, as per your instructions. "You know how you've been saying forever that you wanted to get that unicorn tattoo on your ankle removed, but you thought the procedure would hurt?"

"Yeah," she responds nervously.

"Well, I checked around on the internet for alternative ways to modify bodies. I found this incredible specialist who has a way to release altering chemicals into the body through collars."

"Wait, you mean this guy?"

"Nice to meet you," you say, smiling with all the charm you can manage. "You're girlfriend has told me great things about you."

"No way, this has to be a hoax," says Shelly. Then she looks at the enormous boobs straining Katie's little black t-shirt. "But, well, how can you have changed this much since this yesterday? No, no way, it can't be true."

"It's totally true!" says Katie with an encouraging smile. "I didn't tell you because I wanted it to be a surprise, but I've spent three weeks checking his references." She turns to you. "Can I show her?"

"Absolutely. Just take the collar off and let her put it on."

Katie easily takes off the collar now that she has your permission. She hands it to Shelly and rubs her girlfriend's back reassuringly.

Shelly looks at the collar, clearly unsure what she should do.