Roll After Dark

Oral sex

Mouth on a cock, a cunt, or both.

Why people do it
It is the most direct thing one person can do for another, and it puts one of them physically below the other, which is why so much power play routes through it.
Smallest way in
On the terms you already use, with one change: whoever is receiving decides when it stops.
What to watch
Deep throat is a skill with a gag reflex attached — hands stay free, and pulling off is always allowed. Nothing that impairs breathing.
In the planner
20 different things carry this tag, and switching it off removes every one of them. The mildest of them sits at medium.