Long ago, two races used Earth as their battle grounds: DEMONS and ANGELS:

One day, the humans became tired and angry of them using their home for their eternal war.

So they sealed both creatures underground with a magic spell, hoping they will learn to settle their differences elsewhere.

Many years later...

Mt. Purgatory 201X

Legends say that those who climb the mountain never return.

It was early in the morning. Sans woke up with a groan. The first thing he noticed was how his body ached. He ached all over and his whole body felt hot. His breathing was almost like panting. But he managed to get out of bed. Sans felt fuzzy in his head, almost like he was buzzed. But of course, being a demon he can choose whether to get affected by alcohol or not.

So he wasn't drunk, he didn't drink last night. Then what in the underground was wrong with him this morning? Sans thought to himself while he got dressed. He got his boxers on, pants, and finally buttoned up his shirt. He felt a little dizzy as he got his gloves and boots on.

Sans felt weak as he went out of his room and down the stairs. Papyrus must be in the kitchen, right? Wait, what time is it anyways? Sans let out a loud yawn. He was just about to enter the kitchen. A cold drink may help how hot he felt.

"Sans? Is that you? You're up very early. Are you alright?" Papyrus called out to his brother.

Sans's whole body stiffened in response to Papyrus's voice. His small duel wings fluttered a bit under his shirt. Sans's body grew hotter in response, sweating now. His eye lights disappeared as he figured out what was wrong with him this morning.

Sans was in heat.

Now, being an incubus demon monster, heat is very different. Unlike the usual heat, the incubus/succubus usually has a steady supply of human energy they feed off of. But being in the underground, there wasn't many humans around for Sans to feed off of. So he's been taking what he could get from friends. A hug here, a kiss there, and he can get by.

So when an incubus is in heat, it's really more like when a human has adrenaline. Its a last line of survival when in danger. And boy was Sans really low on health. But he couldn't let Papyrus know that! Pap would try to help him, and he just couldn't do that to his brother. He wasn't himself when this sort of thing happened. He just couldn't do such horrible things to his angel brother.

"Sans? Seriously, are you ok?" Papyrus asked as he came out of the kitchen. Sans was at the bottom of the steps. He turned his head and looked at him.

"P-Papyrus." Sans let out as his body began to shake a little. His head screamed at him to run but his body wasn't working.

"Oh my gosh! Sans! You don't look well. Are you ok!?" Papyrus exclaimed as he rushed over to Sans. Sans backed up.

"NO! D-Don't come near me." Sans yelled out. Papyrus paused in his steps, a confused look on his face. Sans was obviously not well. Why would he not want the heavenly Papyrus's help?

Sans looked around for a way out and locked eyes on the door. "I... I have to go see Grillby!" He quickly exclaimed and then ran to the door.

Papyrus wouldn't stand for this! Sans was not well and should not be going to Grillby's! Sans needed to stay here and let Papyrus help make him get better. He was tired of Sans keeping so much from him. So Papyrus, in one swift motion, spread out his white wings and flew in front of the door, efficiently blocking Sans.

Sans bumped into Papyrus and was knocked back onto his tail and pelvis bone. "Ah!" A small moan left Sans's mouth from the touch. Even if it was through the cloth of Papyrus's robes.

"Sans, look at me." Papyrus said. Sans was looking away at the side, but turned to look Papyrus. He nearly melted at the concerned look on his brother's face. He could feel his magic spread through his body, pooling at his face in a blush.

"Please tell me what's wrong. You never tell me anything. I know what being an incubus demon means, Sans. I'm not stupid. Something's wrong, isn't it? Please let me help you with it." Papyrus said with a sad expression.

"Pap... I... I'm in heat. I don't want to hurt you Pap. Please, just... let me go see Grillby. He'll help me out and then I'll be fine." Sans pleaded. He reached a hand up to Papyrus to grab at his clothes, but decided against it.

What Sans said took a second to process in Papyrus's mind. Once it did, his eyes widened in terror. The tall angel skeleton grabbed Sans and picked him up. Their faces now close to each other, which just caused Sans's blush to spread.

"You're in heat!? But for an incubus that means-... SANS YOU NEED HELP RIGHT NOW! Come on!" Papyrus exclaimed. He then held Sans bridle style close to his chest, and began heading upstairs.

"Wait! Papryus please! Don't-... ah... don't do this. L-Let me... oh... let me see Grillby." Sans pleaded, trying to squirm out of his brother's grip. That was a mistake. His body was so sensitive right now. And Papyrus was just radiating love for him. It pushed him over the edge.

Sans wrapped his arms around Papyrus's neck. With his eyes half lidded and a deep blush across his face, he looked love drunk. His eye lights turned into little hearts as he brushed Papyrus's hood aside to slowly lick Papyrus's neck bones.

Papyrus stopped as a chill went down his spine from the licking. "NYEH! S-Sans! Please, wait until we get into the room. Then I'll... nnh... I'll be able to help you." Pap said as the short incubus continued the attack on his neck. He then continued on his way to his bedroom.

"No Papy. I can make it to Grillby's. Let me go. I can't do this to you." Sans said in between his licks and nibbles. That may be what his head said, but his body was saying the complete opposite.

"No way Sans! You'll dust before you even reach the door. I know what an incubus heat means. You NEED to have sex with someone and I'm the only one here. And I'm not going to loose you Sans. I refuse to loose you." Papyrus said. He stopped and gave Sans a look when they reached his door, making sure Sans was looking at him.

It was so confident and determined. And it show how he loved Sans so much. Sans couldn't say no to him. But he still begged him not to do this, as he gave kisses to his brother's neck. There was no feeling behind his pleads though. Sans's magic began to pool at his pelvis as they got closer to Papyrus's bed. The crotch of his pants now glowing blue underneath.

Sans didn't want to let go of Papyrus when he was placed on the bed. But when he was on the bed, he writhed and squirmed. He was panting, his body spread out over the bed. He gave Papyrus the most bedroom eyes look. It made Papyrus blush furiously in response. Sans is a love starved incubus and it showed big time.