I love most of that.
A few things I’m not too keen on. First is his soul being sold for business success. That’s not really a “I’m going to run away to my brother” kind of offense. That’s more of a “I’m going to call the city guard on you, you sicko psychopath!”
But if it was something like his father, or whoever, failed in their bargain with the Thayan, and the Thayan came for his child as payment, that would make sense. Kind of like a rumplestilskin thing.
The other thing is the rituals his uncle did, and how the Thayan planned to use him. I’m thinking of going a little simpler. Perhaps, like you said, had Titus been trained, he’d have been a great wizard. Maybe what the Thayan did was weave almost a Familiar type ritual onto him, bonding the two of them. The more magic Titus wields, the stronger the bond. The bond would allow the Thayan to see through his senses, to control or twist his thoughts, and for Titus to obey his every whim. That would put a Noble of Watergate under the control of a Red Wizard.
What his Uncle did was to try to sever that bond, but he could only do it partially. The Thayan cannot manipulate his thoughts directly anymore. Also, he cannot automatically see through his senses unless allowed, or maybe only when Titus is in certain conditions.
To weaken the link further, his uncle tried to keep him from learning magic. Maybe he put a mental block on Titus, making him have a hard time learning spells, except rituals, which he could refer to a book to do while he did so, precluding the need to memorize them. I remember at the beginning that I had written that he had trouble with spells, and only could ever do rituals because he didn’t do well with normal spells, so this keeps with that.
Now, perhaps one of the only times the Thayan can contact him is when he is on death’s door. By choosing to talk to him, by choosing to learn from him, Titus accidentally crushes that mental block keeping him from learning spells, and opens himself up to the Thayan. The Red Wizard still cant directly control him, Titus has his own agency and can be his own person, but the Thayan wants him for some reason that only the DM knows. And he wants Titus powerful, again for some strange reason. Only now, he has to convince Titus to serve him, instead of demanding it. With Titus being afraid of death, offering the power to stave it off would be mighty tempting.
As for becoming a Lich after death, maybe that’s part of it, but I almost see it as “You’ll serve me in life or death, I care not which” sort of deal, rather than the end goal.
