The collar did the work.
He only had to abduct her for three days. No one even noticed she was gone. He dragged her, kicking and struggling, his hand over her mouth, out of her home and over to his van on a Friday night, and he welded the thick metal collar in place around her neck right then and there. Then he bound her, gagged her, and spent the weekend driving her around while the collar did its work. He didn't rape her, of course. The first time he fucked her, she was going to ask for it.
The collar had two functions. The first was temporary, and it eventually wouldn't be needed. It simply ensured that when she raised her hands to the collar, to touch it or try and remove it, it would deliver a mild electro-shock, like a dog's obedience collar.
The second would continue for as long as she wore it. During set periods -- constantly at the beginning, but eventually only while she slept - it played quiet hypnotic white noise, just loud enough for her to hear, making it hard for her to think straight and embedding deep hypnotic triggers within her.
For now he only needed three thoughts in her head:
"Don't let your collar be removed."
"You will panic if someone tries to remove your collar."
"The collar was your idea."
By the end of three days she couldn't have touched her collar even if she wanted to - which she didn't. He tried to forcibly lift her hand to her neck before he returned her to her house, and she freaked out and started screaming into her gag, driven wild by the fear of electro-shock and the dictates of her conditioning. Satisfied, he released her, allowing her to return to her own home. And then he communicated with her collar by Wi-Fi, and uploaded her real conditioning schedule.
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She didn't remember why she had wanted the collar, but she knew it had been her idea. She didn't like the not knowing, so she rationalised to herself that she liked wearing the collar and looked pretty in it, and soon she truly believed this to be the case.
Over the next few weeks she found herself in odd moments browsing porn on the internet, looking for pictures of girls in collars like hers. She would self-select among these pictures for the girls who looked most degraded, most humiliated, and who had the biggest tits, and then she would masturbate to the verge of orgasm while staring at them. This was new for her, as she had never been into either girls or porn previously, but the images of big-titted sluts in collars drove her wild. Without quite knowing what she was doing, she arranged colour prints of some of them and Blu-Tacced them to her bedroom wall. She would look at them each morning and note the ways in which she was different from, and therefore inferior to, the girls in the photos.