A/n: FUCK it this is my book and I'm gonna write fontcest because why the fucking hell not? I need more inspiration for ideas or I'm gonna write more weird shit like this book. Kk bai

Sans pov

It was this time of month again... the time when i was in heat... the thing is, the only person i want to help me is my brother but he wouldn't help.. i didn't want papy to help... i didn't want to ruin my baby brother's innocence.. Welp... time to pleasure myself again...

I pulled off my shorts and through them god knows where. I grabbed my newly formed ecto-dick and started to rub it up and down. My loud moans filled the room. I'm glad papyrus isn't home to hear me.. he would be in here trying to see what's wrong... SHIT! PAPYRUS IS STILL HERE!  I shove a pillow in my mouth to shut me up until I heard the door being smashed open and my brother staring at me...

Papyrus pov

I the great papyrus have been taught a new spaghetti recipe by undyne! I was starting to create this masterpiece for my brother until I heard strange sounds come from his room.

Curiosity got the best of me as I climbed the stairs to my brothers room. I tried the door. Locked. I took it upon myself to kick down the door.

I stared in shock. How couldn't I? I saw my brothers shorts on the floor and sans was biting a pillow with his hands around a... blue thing that was letting blue liquid out of it? I was confused and also I bit concerned. Was sans ok? Was he ill? Did he need the great papyrus' help?

As I questioned what was happening, I felt myself being pinned against a bed and the door being shut and locked behind me. I looked at sans as he was on top of me. His left eye was glowing blue and he was sweating lots.

"B-BROTHER? ARE YOU OK? DO YOU NEED THE GRRRRRRRRREAT PAPYRUS' HELP?" I asked as I looked up at my bro.

"Heh... your too cute pap... ive stopped myself for so long... I can't fight it anymore... I love you papyrus." I was about to answer sans as he shoved his teeth against mine as a sort of skeleton kiss. I felt something slimey run along my bottom teeth. I was confused but didn't move. Sans growled and he ran his fingers along my spine, making me moan. He took this chance to plunge his tongue into my cavern and explore his new territory.

As sans pulled away, I felt... heated... I looked at my brother as he started to take my clothes off. My battle body and shorts, leaving me bare. He looked at me for a second before grabbing my ribs and spine, sucking, biting and licking everything he could. I moaned loud. He looked up at me and smirked with those sexy eyes of his.

Unknowingly, I summoned an ecto-pussy. Sans seemed to notice as he kneels down and started licking the clit. I moaned and bucked my pelvis up  making him stick his whole tongue in me. I moaned as he started eating me up and thrusting his tongue in and out of me, making me moan and be completely at his mercy. I felt a knot in my stomach. As it realised,  I moaned and sans started using the fluid to rub it on his ecto-dick.

"Hehe~ This might hurt a bit bro but I promise it will turn into pleasure soon..." as soon as he finished his words, he trusted into me. I screamed at the top of my nonexisting lungs in pain as my brother kissed me to calm me down.

After a few minutes, all the pain had turned to pleasure. I thrusted up to feel immense amounts of pleasure. Sans took this as a sign and started pounding into me with no mercy. We were both moaning a mess until I felt the knot again, but bigger.

" S-S-SANS~ IM GOING TO~"

"same bro~ cum with me~" we moaned each others names as we cummed at the same time. Sans' eye stopped glowing as he slumpped next to me.

"Sorry about that bro.. ive been in heat and I didn't know how to deal with it."

"ITS OK BROTHER. I THE GRRRRRRREAT PAPYRUS WILL ALWAYS HELP YOU!"

"Heh... your the coolest pap... love ya." He said as he let sleep take over. I signed and kissed sans on the forehead.

"I LOVE YOU SANS... I ALWAYS WILL.." I kissed my brothers forehead as I let sleep take over.

A/n I know I know... this is a reader X undertale au s book... SCREW YOU GUYS THIS IS MY BOOK AND I CAN WROTE WHATEVER I WANT! Anyway... I hope you enjoyed and please leave comments on what I should write next! Until next time my lovely sinners...
Peace out
- author-chan

(P.S. 845 letters)