imagine a reality where peeing isn't a multiple times daily endeavour, more like a once a week occurrence. people's bladder capacity increase massively, meaning that holds last more than just a few hours... more like a few weeks.
now imagine someone who has been holding for a month or so now, they've lost count of the days by now. they've either been forced by a lover who just wants to see their vulnerability in its rawest form, or maybe a little twisted wire in their brain makes the feeling of an overly full bladder pleasurable for themselves.
each day is almost torturous for them. they've always been known to have a huge bladder capacity — peeing is a very rare occurance for them — however, this is a whole new story. their bladder bulges out, almost like a shelf, making them look pregnant. because of this, they have to wear dresses/trousers with loose waistbands, fearing that even the slightest bit of pressure around their full abdomen will cause the ocean of pee to hiss out of them.
their peehole aches needily, fluttering each time they sit and push on their bladder accidentally. daily tasks like showering, cleaning, exercising have become agonising, even leaving tiny (and unrelieving) wet spots on their clothing closer to the end of the month.
with the scenario of a lover forcing them to do this... they press on their bladder "accidentally", poking and prodding the dense and tough ball of hot liquid in their lower abdomen. towards the inevitable end of the hold, each poke causes a leak to gush into their clothes, but no matter what pained noise leaves their lips, their lover denies them relief.
now imagine the end of the hold. maybe the person's out somewhere: shopping, university, a friend's house, public transport. they can tell that they're nearing the end of their hold. although the pride they feel when their bladder bulge is praised/compared to a pregnancy bump, they know that their body will give out at any point. the worst thing is... due to the low frequency that people use the bathroom in this reality, they're not readily available anywhere. and they can tell that they're going to lose it any second.
peehole fluttering, leaks gushing out into their clothes every few seconds, the person's reduced to a shaking, blushing mess, knees buckling with the weight of their overfilled bladder. they either miraculously find a quiet corner where they can peacefully let out a whole month's worth of urine (and are soon found by onlookers of the huge puddle of pee that's slowly making its way into the public, revealing the person's sick interests).
...or, their bladder's had enough. pain shoots up through them with every attempt of a step forward towards a quiet corner... it's useless. the month's worth of urine is coming out now, no matter if they try to stop it or not. they crouch down, gallons and gallons of hot piss hissing out onto the linoleum floors of a mall/university classroom, or they put their head into their hands as they gush helplessly into the plush seating of a friends' bed/couch or a seat on public transport.
they are soaked, bladder aching once they're finally empty for the first time that month. it took damn near 10 minutes of gushing wherever they may be to void their bladder, and, although they're a blushy, embarrassed mess, they can't deny the feeling of satisfaction and desire they feel once they see their mess, no matter how many onlookers were there to see their moment of weakness.