imagine you're a succubus assigned to the royal kennels—at first you're confused about why you were picked; you like hellhounds just fine but you have no particular aptitude for their language or care. but on your first day the answer becomes obvious: they're in heat. within your first week on the job, you get curious enough about their thick, dripping cocks to let one breed you, and by the end of the second week, they've all taken a turn, knotting you one or sometimes two at a time and pumping you full of hot, potent cum. they keep doing this for the duration of their heats, and by the time a few months have passed, it becomes apparent that your belly is swollen with more than just cum. since the pups are healthy, the kennelmaster decides that this is a win-win: your appetites are sated and the hounds have a convenient way to sate their own lusts. every few months, your belly swells with a fresh litter, and every time the hounds are in heat, you offer yourself up as a hole to fuck and a womb to fill.
one day the kennelmaster summons you to his chambers for a special assignment: one of the three-headed kerberos demons that guards the palace is going into heat, something that only happens once every century or so, and they need a willing mate for the duration. you're more than happy to volunteer, of course, and when you discover that the kerberos demon has an even bigger and thicker cock than the hounds you're used to fucking, you're practically desperate to take on the challenge. and it is one: it takes them hours to work you open wide enough to fit their cock halfway inside of you, and then more hours of relentless, steady fucking before you're stretched enough for them to bottom out, their cock fully sheathed inside of you. by the time their rhythm is starting to falter, you're relaxed enough that the head of their cock is sliding in and out of your cervix, and when they finally shove in one last time and start to come, their knot expanding to tie the two of you together, their cock is halfway inside of your womb.
of course, there's no chance that you aren't knocked up, with a belly so full of their warm, fresh seed and more getting pumped into you by the second as you clench around their still-growing knot. you can even feel your cervix clutching and twitching around the head of their cock where it's locked inside of you, pumping cum directly into your womb: stretched as you are, you can feel every spurt, and your belly is starting to swell already from how full it is. not that it matters—this is just the first day of their heat, which usually lasts for at least a month, so even if you aren't pregnant already, you certainly will be by the time they're done with you. you try to imagine how big your belly will be after a month of getting relentlessly fucked and pumped full of cum every few hours, and shiver with pleasure. you've come such a long way from that first confused day at the kennels; now look at you! the perfect breeding bitch: knotted and filled and still desperate for more.