I've seen a few things about fantasy omorashi curses lately, so here are some more 🪄💧:
You can only pee when your bladder is 100% at its limit (when it normally would start coming out on its own without your control). You don't get any special knowledge of when that is, just the regular feeling of desperation. If you try to go to the bathroom, even if you're 99% full, you won't be able to get any out. When you hit 100%, your bladder automatically empties itself completely, regardless of where you are.
You can pee whenever you want, but it comes out one literal drip (~0.05mL) at a time, maybe 2 drips per second if you're lucky, 1 drip per second or even longer if you've really pissed off the curse caster. If your max bladder capacity is 500mL, it would take almost an hour and a half to empty completely at 2 drips a second. You could only get about 30mL out in a regular 5-minute bathroom trip. To keep a regular schedule, you would often have to stop the flow and go about your day, still full to the brim but out of time to empty. And then when you're absolutely desperate, having to suffer through the torment of that desperation releasing itself one...drip...at...a...time...
The person who casts the curse picks an activity of daily living (eating, walking, speaking, etc.: let's say sleeping for this scenario), and now you can only do it if your bladder is at least 75% full. You literally, physically won't be able to do the activity if you're less full than that. Now, when you're tired, you have to drink a bunch and wait to fill up, then get in bed uncomfortably full and try to fall asleep. You'll have to get over your anxiety about wetting the bed, because no matter how tired you are, you physically can't sleep unless you have to pee, so having insomnia from your full bladder just won't do. Maybe sometimes you do wet the bed and then instantly wake up, unable to go back to sleep until you fill yourself up again.
You can only pee if someone else is pressing on your bladder for you. Otherwise, the curse makes your bladder and torso expand indefinitely, so you'll hold it without bursting until you can get someone to help, but you'll be in absolute agony. And how embarrassing and heavy it would be to walk around with a bladder bulge the size of a yoga ball. It's an okay curse if you have a willing friend or partner, but what if you live alone? What about at work? What if you're home alone for the day (or the week)? How would you find someone to help you?
You wake up every morning with a different bladder capacity, but there's no way (except trial & error) to tell what it is. Some days it's huge and you can hold a gallon of water just fine. Other days you have half a cup of coffee and you're wetting yourself. The curse also makes you very thirsty, so avoiding drinks altogether isn't an option. You just have to drink very carefully and hope to hell whenever you take a sip of something that there's a bathroom readily available in case it fills your bladder way more than you were expecting.
Feel free to elaborate on any of these, add your own, or use them for stories 😉. Maybe I'll do more later.