Try the transformation option, both body and mind

The collar seems to work, but maybe she was just giving her honest opinion. It's time for a serious test, one that couldn't possibly work with a normal piece of leather.

"I wish you had huge breasts."

"What?!" she yells. "Oh, real nice, you perv. What do you think-"

Suddenly the dark haired girl drops silent. She looks down at her chest and watches as her loose black t-shirt fills out. Within a few seconds she goes from breasts so small they don't need a bra to big, perky melons. The little shirt rises up, showing off her toned midriff. Combined with the short, black leather skirt and fishnet stockings she was already wearing, she's dressed to kill.

Her eyes look like she's about to kill, too.

"What the fuck! How did you...? It's this collar!" She starts clawing at the collar, but it won't come off. People around the mall start to look as she yells, "You asshole! I'm going to-"

"I wish you'd calm down and stop resisting!" you hastily spit out.

Her hands drop to her sides and her expression becomes totally tranquil. She looks at you with mild disinterest and says, "Okay."

"Uh, okay what?" you ask.

"Just, okay. You changed my breasts somehow, and I'm sure my girlfriend will freak out, but I guess that's fine."

Wow. When she stops resisting, she stops completely. And she has a girlfriend? That's worth investigating, but right now it's worth seeing just how little resistance she has. "Hey, you want to come back to my place?"

"Sure. What are we gonna do?"

"Well, how about you spend the rest of your life sucking my cock like a good little slut?"

"Sure, whatever you want," she says as if you'd just suggested getting pizza instead of Chinese food.

You lead her to your car, then drive her back to your apartment. She doesn't say anything for the whole trip, just stares out the window with a bored expression. You use the time to plan.

As soon as the two of you walk through the door she says, "So, I suppose you want me to start sucking now?"