Succubus/incubus: another useless dichotomy
Most people find this out when they're approached by a handsome stranger in a dark, crowded bar.
They might be briefly surprised when the broad shoulders and muscled, hairy torso lead to a wet cunt, but even the last little trace of apprehension disappears when they're balls-deep, a low voice grunting and panting right in their ear.
Bodies pressed so closely together, and the stranger's sturdy thighs wrapped around their torso, muscles clenching around their cock, it's hard to notice anything amiss. They can't see the warm, brown eyes flickering bright red as the stranger buries his face in their neck. Can't see lengthening nails digging into their back. Can't see the glowing sigils on the stranger's underbelly, pressed against their own.
In fact, they have no idea at all, returning home that night feeling better than they ever have, if a little dazed.
They start gaining weight, and shrug it off.
Only when they awake one morning to their little pot-belly thrashing and jerking with inhuman ferocity, do they start to understand.
Some might be able to count back to the day they met an unbelievably attractive but slightly... odd stranger and realise it's been about six months. Some can only look in shock at what was a physical impossiblity up until it happened. Some people's denial runs so deep, they never suspect at all until their water breaks.
And all of them will find themselves laboring, looking up at their swollen belly from flat on their back, and seeing a familiar figure appear from nothing to stroke their trembling flesh while wearing a devious smile.
Most people put the memories into a tiny little box on the highest shelf in their mind as soon as the demon leaves.
But the ones who realised with a start that fucking a stranger had made them pregnant... The ones who had spent every second since then replaying that night while feeling their belly move... They might return to that bar in a few months' time, looking around hopefully, core going gooey and cock getting hard when they see familiar red eyes.