Slow burn Demon mind control. (Male demon, female human, heavy smut)

This is an old idea for me, but one I really want to reach the end of. Fairly simple, but it can be quite complex based on how it rolls out as well

Premise: A Demon is accidentally summoned by a young woman, and he proceeds to take his time slowly twisting and breaking her mind to make her his own personal toy.

Now lets expand on this a little bit. 

Pretty much what I'm looking for is a slow, slow burn. Meant to take its time in what happens. Girl summons demon by accident, nothing new there. The idea as a whole isn't new, but the length is what I want. Its slow in how long it takes him to twist her. The demon himself revels in the pleasure it brings him to do this. Sadistic to the core he wants to watch her twist to his desires over time. So instead of having the break happen within the first couple of times, it can be over a long period of time. 

This is an idea that has been burning away at me for a long time. Only prompt I've thought up that I just haven't been able to forget about. 

Everything can be talked about before starting, or if you want to try and make it as spontaneous as the prompt is at its core, just shoot a starter.

If there's anything unclear (as I'm sure I've forgotten some things) don't be afraid to ask.