Sans truly did not understand much at first.
He didn’t understand the sudden absence during your secret nightly visits. He didn’t understand the frequent mood swings you experienced. He didn’t understand how hot your body seemed at times, yet how you weren’t sick. He didn’t understand how loud your soul would beat at times in cold, dead nights.
Then it hit him like a brick.
You are in heat!
Wait…. That didn’t make sense. Humans don’t go into heat.
The primary thing to find out was how.
How can a human go into heat?
Humans don’t use nearly as much magic as monsters. Sans theorized that since you lived in the underground for oh, so long (seven years to be exact) your soul used the strong, thickly essence of magic in the atmosphere to survive long periods of hunger. And since your soul consumed so much magic, it needed a way to dispel. And it did find a way, heat.
The next to find out is would your human heat be the same as monster heat? He expected so. Then it’d be greatly easier to take care of your problem. And stars, he hopes your heat wouldn’t endure long.
The last to find out, are you… home? Your home?
He knows precisely where you sojourn. In a deep cavern just ways off, by the large door the nice (and rather disturbing) matron lived. The way inside held many twisting and turning tunnels that one could get horribly lost and never find a way out. But you’re clever, You know the tunnels like the back of your hand. One of those tunnels led to your compact little home. Since it was remote from the outside, your cove was very warm. There was only a thick mattress, (provided by sans) multiple lush blankets, four fluffy pillows, a journal, some pencils, and a lantern. It was tall enough for him to crawl around in and you to stand that the ceiling just scraped past your head by an inch (his neck would bend if he stood full height). It was wide enough for three of him to sit snugly but that was about it.
He couldn’t think of another place you could be in, so it was a safe bet to assume you were home.
Sans currently laid in bed, eye lights to the ceiling in deep thought. It was night, or what the underground seemed to call night. Night meant everyone was asleep and quiet. No disturbance outside thus everyone can sleep in peace.
Perfect opportunity to meet you.
But he was uncertain you would be at the bridge. Sans twisted over and eyed his bedside clock. He noted the rather late time. Eleven at night. Almost a handful minutes before your secret meetings (he loved those).
You and Sans would meet exactly at eleven-thirty every night. The both of you would usually play in the snow, talk in deep conversations, or cook up a new kind of meat (you’re a fantastic cook). Whatever you guys did, he loved it. It didn’t matter, just as long as he was with you. Sometimes those nights would end with him and you cuddled in sound sleep in your cave or he’d teleport you in his home to slumber together (those nights were the best).
But for the past few days, you asked to end those nights early. And yesterday, you didn’t even show up at all. He was troubled, wondering if you were sick of him. Then he was frightened, did something horrible happen to you?
Monsters devour humans. And although monsters could teleport back and forth to the surface to hunt whenever they pleased, they wouldn’t pass up a human hiding amongst their village. That’s why you both met in secret, he was keeping you safe. And you knew this, thankfully remaining to yourself. Well, except him. Sans was your main source of food income. He brought meat every day. Which reminds him….
If you went into heat, why did your soul still absorb magic?
Sure, he began feeding you just three years ago, but wouldn’t your soul have finished eating? He ended his theory by assuming that your soul continued it’s consumption as a back-up plan, were anything to happen to your food source.
Sans turned in his bed. He hoped you were okay. By the singing of your soul, you were at the beginning of your heat. Sans wasn’t worried about other monsters hearing your soul right now. He always possessed a natural talent to hear even the most quiet souls in the loudest moments. That’s why he was remarkably good at hunting. But your soul remained clamorous.
As far as he knew, there are only four steps to heat.
The first, agitation. Agitation made a monster (or in this case, you) hide away from the public. They were constantly tired and turned away from food. This step lasted in the span of a few days.
Sans eyed the clock again. Eleven twenty-five. He hummed indecisively. He desperately wants to see you, even in your most aggressive mood, he wants to see how you’re managing so far. He needed to prepare to aid you (if you wanted that is). Making up his mind, Sans speedily shoved his slippers on and teleported away.
He wobbled a little as he landed by his sentry point in his flurry.
As Sans hurried through the snow, he then scented a faint, citrine, butterscotch scent intermingled with sweat and tension. His soul responded with interest by pulsing, sending small ripples of signal to the female in heat.
You were merely in step one of heat. The smell wouldn’t affect him sexually except demonstrate interest and exert dominance towards any competitors. Your smell would only change on step three, where it would send very... explicit signals to his soul in an inappropriate manner.
That wouldn't be for a while.
For now, he dug and kicked a line of snow that dipped down to the earth and stretched around the outside of the bridge, forming a half-circle. Then he summoned his soul and marked the line with a small spray. It smelled of heavy testosterone, a salty and almost spicy scent. It conveyed messages to any trespasser to back off. This way, he claimed the territory and the gal in heat just inside the territory line. Sans couldn't imagine any monster would challenge him for it. They must have a death wish. He walked beyond the bridge with his soul out, who continued to spray along the inside of his newly claimed territory, ensuring ownership. He couldn’t wait to see you. It’s only been a day but it’s the most the two of you been apart in two years.
As he arrived at the entrance of your cave, he dispelled his soul back inside his ribcage. He inhaled the now more potent scent of you. He lifted a brow bone.
How the hell did you figure out how to make a scent mark? Scent marks (what Sans just did to the outside of the bridge with his soul) send rather hostile messages. They are claims to possession and usually cause fights amongst monsters. And they are laborious to master. You, meanwhile, arranged so like an expert. Your scent mark perfumed estrogen, sweet and a little tangy.
He felt hesitant now. His soul told him to back off and leave you be for a while, scent marks were no joke. But he still craved to see you, so bracing himself, he entered. He recognized the way into your tiny cave but his soul began to thrum in slight uncertainty. He was a little startled. Even though you were much shorter and more of a lover than a fighter, your scent mark told every fiber of his soul to 'go away' and 'don’t mess with me'. But he continued.
A quarter into your cave, he heard a low growl. Higher pitched than a male would make, it implied a warning. He slowed a bit, stepping lightly. Then he heard the growl go deep and dull. He kenned you, his soul sent friendly, peaceful waves of vibrations to your soul. Your soul responded with fierce, challenging shocks to his.
He didn’t believe this was a solid idea anymore. As he entered your home, he saw a dim, small shadow nestled in blankets and pillows. The figure shifted. It was you, of course. Your hair was knotted horribly, your face dry and drool crusted across your lips. You looked completely different, all except your brilliant dazzling eyes.
“(y/n)!” He exclaimed in relief and growing excitement.
You reacted by slowly rising. A snarl across your lips, eyes shooting daggers. You growled much more boisterous again this time creeping closer to him. Your delicate fingers curled into claws, ready to strike across his skull.
He found the scene quite hilarious, he just had to snicker. He wasn't afraid anymore, he remembered how minute you were compared to him. He was two feet bigger than you, you can’t leave any lasting scars on him. You were so kind and gentle and loving and patient.
Right now though, you looked like you could just about annihilate him. Heats made the host animalistic and impulsive, so he understood your reactions.
“i’m so glad you’re safe.” He sighed, acknowledging that you couldn’t understand him right now.
You crept closer and snarled, your soul abandoning the security of your body and whirring to fight. Sans's soul came out with similar buzzes. The souls were challenging each other.
Sans wasn’t afraid, he could handle-
His right leg was yanked forward so swiftly that his skull thunked against the hard dirt underneath. You mounted and pinned him down, growling loudly. Sans blinked, dazed over what just happened before your nails raked across his face. He winced, that hurt! He took the liberty to flip both of you over so that he pinned you underneath instead.
“okay, that’s enough-” He didn’t get to finish before your feet stretched up and struck his nasal hole so hard, he let you go. He groaned and clutched his face. You returned with two more strikes across his eye sockets with your powerful, rather sharp nails.
Sans yielded and teleported outside your den. His face stung like hell. Yup, that was a mistake.
He eyed the dark, dreary den once more. He’ll check up on you later. Right now, he thinks he needs some bandages.
You groaned as another wave of unadulterated pain spread across your uterus, shaking your inner vaginal walls in agony. You writhed around your hand-me-down mattress, wrapped in thick blankets (the only thing bringing you comfort). Your entire body felt unusually hot, beads of sweat formed behind your neck, armpits, thighs, forehead and between several folds of your body. You gagged often, unsure if you needed to vomit. This is nothing like you ever experienced before. For a moment, you thought you ate a rotten rabbit or a diseased deer. Then you began to think it was some form of cancer, a tumor slowly killing you minute by minute.
You counted on the tumor.