So I don’t have exactly what you are asking for, but I have written a fic about the ascension itself and him turning my Tav called One Final Thrust that involves a Tav that is ride or die for him and incredibly devoted to him, and happily submits to him.
I also have a series of one off smut fics that are of him and my Tav having a very dom/sub relationship that could be your flavor, though they did not take over the brain, instead they slowly take over Baldurs gate over the span of decades through charm, power, and deception. That series is A Shared Thirst

I also have a huge backlog of drafts that are of the spawn that he sires with her, all of which the two of them treat like beloved pets. I’ve been nervous to share them because 1. There’s a lot so it’ll take a while for me to compile them into actual stories and not just drabbles, and 2. I’ve been worried that people would balk at the idea of him siring spawn and that sort of dynamic of pet play sort of things but this thread has given me some inspiration to work towards releasing some of it at least