@ralord82276This is excellent.
I could absolutely dig "vampiric voyeurism" and actually relate.
I think the need to physically see the object character could be one of the aspects where the growth of his power could be apparent. At first he must establish eye contact to get "in" and it's just a fleeting glimpse of the inner other. Then, he can follow for a period afterwards an eye contact. Then, just intense watching over relatively short distance and for quite a while is enough to get in, then he can just look at someone and establish contact, at a growing distance and decreasing observation time.
Then, he can follow the ride even out of sight as long he's certain of the exact location. That's boosted with, necessarily, the visual input from the ride's own eyes. Darkness, shut eyes, looking at a phone screen while walking, and similar could be very confusing and easily break the connection. Also an area of gradual improvement. And again, only within a certain, initially small range. That could grow, eventually, up to about half a mile at a maximum, but no further.
Any forms of such advanced deep riding would necessarily require a lot of concentration and come at expense of almost completely losing own sensory inputs in the meantime, appearing to be in a transe like state that's easily distracted. And a ride out of sight can not be re-aqurred if connection is lost due to a personal distraction.
The ultimate could be ability to jump from one ride to another by establishing eye contact with the new target from the current ride's eyes, perhaps eventually even if the new target isn't in direct sight themselves, but all the previous limitations apply. Plus, it perhaps could only work with "familiar" persons he had been already "visited" directly before.
This could be a theme, that it's increasingly easy to ride familiar people while new contacts require full sequence, with direct eye contact at short distance to open the gates the first time. With training, the routine after that could be fast and increasingly simple, but even just that requirement could be significantly limiting, especially in the later stages when he could otherwise control groups of people from afar.
On the voyeur side of things, and planting my own kinks, I would introduce nudity of the target as both significant boost and a factor that ease acquisition of the contract. It rhyme with the sexual theme but isn't exactly the same.
Alternatively/additionally, he could discovered that it's much easier to "wear" others and boost the experience and depth of influence, especially into the sexual, if he himself is naked while doing so. While kinky and enjoyable on its own at first, that could become an additional necessarily cost, especially for long distance multi target feats. Again, limiting the utility of those for "other" purposes. However, at same point he could be as (over) confident that to believe he could make people to ignore or accept his nudity upon discovery. It could also serve as additional incentive to try to establish clothing optional lifestyle around himself.
I think his influence could never be direct and accurate. He couldn't force one to perform certain actions puppet-like, or put exact words in their mouth. He could only nudge and assist, and perhaps plant ideas that should then germinate in the targeted person's own mind before they're acted upon. It's not a fast or straight forward process, but subtle, and sneaky, but then accepted as person's own.
At advanced stages, he could have ability to search the person's memory for moments supporting his objective and even subtly manipulate the recalled memory to better suit his goals. Like, instead of forcing a girl to take off her swimsuit -- something that's expensive in energy and may or not work at all --, he could convince her that she had wanted to go nude on the beach at a previous instance already, but only chickened out because of obstacles not present currently, so there's a chance to try it now. Or, instead of forcing her to flash a guy and the submit to his advances, he would search for instances she had thought positively and wanton towards the guy and nudge her to act on those latent desires. Necessitating presence of such a nugget in her mind, of course; if she's unconditionally revolted over the guy, we're out of luck and now only reinforced that, but it likely wouldn't have worked anyway.
And yes, there could -- shoul -- be a problem of balancing the "energy" expenditure for establishing and maintaining contact, and -- especially -- influencing the target, with the payoff from the eventual emotional experience of the target. And that should be positive for maximum value.
He could discover the hard way that hard abuse of the target or forcing them perform far out their comfort zone, making them upset with themselves, questioning own sanity in a bad way, essentially performing a distance rape, could be far more draining than anything. While bad emotions are still emotions and powerful enough responses could gain a small positive outcome even in the negative, it's nowhere near the potential of a positive, joyful experience. Even if the negative could perhaps been simpler, but not necessarily easier to trigger.
Since it's the emotional impact of the experience of the target that count, persons could be potentially "raided out" especially if mistreated. Take sexual escapades escalate too fast, train her into a complete slut, and sex is now mundane activity for her and while fun by far not that anymore. He could jump into the guy, there's likely some excitement to had, but if she's a known slut, even that could numb. Even worse with humiliation. The victim would just shut down and go to the inner refuge and there would be no return.