Really big fan of when girls aren't allowed to pee or are physically prevented from doing so. Anything ranging from punishments(either minor kinky stuff or wide scale laws) to literally plugging a girl shut. Usually the latter is paired with hyperdesp, so her bladder just gets progressively more full but it's just agony, no health complications, personally I kinda like when she's aware of how bad this could potentially be for her if she doesn't get permission.
Willing holding sessions are hot in real life, but for fantasy I want some power imbalance, a bit of torture.