All of the Roys are obsessed with power (getting it, keeping it) to some extent. This is obvious given the show is premised on a power struggle over control of Logan's media empire. Kendall clearly wants power, but his vices keep him from ever truly having it (at least on his father's terms). Shiv likes to pretend she's above the power struggle, but is helping run a presidential campaign, a much bigger contest for power until she gets dragged into the family struggle herself. She also married Tom, who is often subservient to Shiv's desires and goals (in part due to his own incompetence), allowing her to wield virtually all of the power in her private life. Even the oft forgotten Connor, closed off from the power struggle as The Unfavorite, makes a presidential bid in his attempt at claiming power since he can't get it from his father. Not to mention his most fulfilling relationship is the one he has with Willa, who as an escort paid to please and spend time with him, can never be his true equal within the relationship.
But it is often hard to understand Roman's take on power. As the family screw-up, he was never seriously considered by Logan, his siblings, and even himself to take over (at least not until Shiv and Kendall mess up so royally as to ruin their own chances.) But he is equally unafraid of flaunting his power and influence as a wealthy heir to a media juggernaut. Yet, that isn't unique to Roman (though his particular brand of cruelty in doing so may be). So what's Roman's particular manifestation of his anxieties about power?
In his sexual kinks.
Both of Roman's revealed sexual fantasies center around the paradoxes of power he exists within. Gerri degrading him and calling him worthless allows Roman to play out a fantasy in which he truly is powerless. Because no matter how marginalized he may be in his own family, he will always be able to wield power in the world due to his name. His interest in necrophilia-play allows him to play out the fantasy of him having total control over another person, given that his domineering father assumes control over all of his children's lives, denying them of it. The sexual gratification Roman feels because of these acts has less to do about the "sexiness" of the situations, made very apparent by his inability to get it up under more "vanilla" circumstances. He derives pleasure specifically out of the power imbalances he is unable to experience in his own day-to-day life.
Gerri goes along with it (despite all signals indicating that she would most definitely not be into it) because it allows her to live out a similar fantasy. As Logan's long time shadow fixer, Gerri is the reasonable non-family successor to the enterprise, yet every time he brings her name up, Roy treats her as nothing more than a placeholder for appearances, while he grooms his arguably less competent children. Gerri is deeply aware that she will always be tangential to real power. So she's able to live out the fantasy of being dominant (over a Roy no less) through her interactions with Roman. That's why the two work together so well: the other has the one thing barring them from gaining true power in the company. Gerri lacks the familial tie to get power within the company. And Roman lacks the competence and focus to do the unglamorous business parts of the job.
