One day, in Hotland...

"Papy dear, could you come here for a sec?" Mettaton called from the Lab. Papyrus was outside, practicing his attacks. He, of course, was extremely focused on becoming a royal guard, so he practiced his attacks in Hotland, for endurance purposes. "SURE METTATON! I'LL BE RIGHT THERE!" With one last random blast from the Gaster Blaster, he entered the lab. "I UNDERSTAND THAT THE GREAT PRESENCE OF I, THE GREAT PAPYRUS, IS NEEDED." Papyrus looked around. He couldn't find Mettaton. Looking down, he saw a trail of something strange. "WHAT THE-" Papyrus was interrupted by the sound of Mettaton's heavy breathing. Frightened, Papyrus rushed towards the sound. Finally, he reached a door he hadn't known was there, and forced it open with a strong kick. "METTATON! ARE YOU ALRI-" Papyrus couldn't finish his sentence. On the floor was Mettaton, legs spread and leaking from... Where? "M-METTATON! W-WHAT HAPPENED?" Papyrus asked. "Pap-Papyrus... Please... Help me..." Papyrus rushed to Mettaton, lifting his head. "WHAT HAPPENED? WHY ARE YOU LIKE THIS?" Mettaton was panting, eyes filled with oily tears. "I-I need... You..."
"NEED ME TO WHAT?!"
"I need you to..."
Mettaton grabbed Papyrus' hand, holding it to his face.
"I need you to..."
Suddenly, he yanked Papyrus' bony hand down to his metal bulge.
"I need you to FUCK ME!" Mettaton broke into a fake sob. "It's been sooooo LONG! I've been craving your giant bone for ages! If I don't get it now, I'll die of mal-bone-trition!" Mettaton went from sprinkling tears to a seductive smile. "Don't act like you haven't craved my shiny pink ass all this while." He lightly pressed on Papyrus' "Giant Bone". "I-YOU-US-MY.... WHAT?" "My my, am I just too fabulous for words? Or..." Without notice, Mettaton grabbed Papyrus' arm and flipped him around, then, with his legs, cushioned Papyrus' fall and settled him down onto the floor. (Because Mettaton is just fabulous enough to do that.)
Soon, he was hovering over Papyrus, who was quivering out of sudden shock. "M-M-METTATON! I-IM NOT R-READY FOR THIS!"
"Oh Darling, are we ever ready? Just enjoy it raw, like I do." Licking his lips, Mettaton lowered himself to Papyrus' neck. He began licking the bones, up to his eye socket. "I don't suppose it would hurt if I..." Leaving his thought unfinished, Mettaton stuck his tongue into Papyrus' eyeless hole. Papyrus gasped, and covered his mouth, although it didn't help much to stifle his moans, since they echoed through his skull. His moans vibrated in Mettaton's mouth. "Mmmhmm~" Mettaton moaned. Papyrus, as soft-hearted as he was, didn't want to feel good by himself, so he moved his hand to cup Mettaton's behind. Of course, he knew one hand wouldn't do for Mettaton, and Mettaton didn't hesitate to grab Papyrus' hand to put alongside the other. Papyrus was limp at first, but soon, he began massaging the steel frame of Mettaton's bosom. Mettaton paused to praise Papyrus. "Ahhh! Yes! Just like that!" He yelled seductively. "M-M-METTATON?" Papyrus asked quietly. "Yes, my big hunky skeleton?" Without words, Papyrus took one hand and pointed towards his "giant bone", which had been left untouched once Mettaton had begun on his neck. Without saying, Mettaton already knew what to do. Mettaton turned his body around, so that his metal parts would be on Papyrus' face whilst he was face-to-face with Papyrus' protruding bone. Slowly, he started from the bottom and licked up to the top. Papyrus violently shook, not sure how to feel. The clattering of teeth was like music to Mettaton's ears, because he knew that Papyrus wasn't shaking out of fear or cold, but out of how good he was feeling. How good HE was making him feel. Papyrus was still hesitant, but with a little bit courage, he took the leap and licked Mettaton from his middle to the middle of his metalic ass. While Papyrus was shaking out of his bones, for Mettaton, it took little-to-no time at all for him to fully consume Papyrus into his mouth. He didn't begin moving, however, until he felt Papyrus rolling his tongue around the dent of his behind. Mettaton jolted, and was put into action, dragging up and down Papyrus' outstanding bone. "M-METTATON! AHHHH!" Papyrus yelped. "Mmhmhmhm~" Was the only response Mettaton could give, as he sucked on Papyrus with utmost priority. Mettaton backed up into Papyrus' face, giving him more to work with. "MMMHMMM!" Papyrus continued to roll his tongue, then licking up and down Mettaton's ass crack. Papyrus smacked Mettaton's behind, and the vibration of the echoing metal only made Mettaton feel it more as he traced up and down Papyrus' colossal boner. Suddenly, they heard the sound of the giant Lab door opening. "hello? anybody here?" Sans called. Papyrus and Mettaton both stopped and listened in horror as Sans made his way towards the door they we shaking behind. Quickly, they both sat upright and fought to find a good explanation for Papyrus' enraged bone and Mettaton with his oil leaking everywhere. They heard Sans as his footsteps got closer and stopped right in front of that room. "what the... why is there so much oil here? mettaton, you in there? paps with ya?" Mettaton was quiet almost knowing what would happen next "O-OH UM YESS WE ARE PRESENT AT THE UM MOMENT SANS.' Papyrus said hurriedly making the situation 100× more awkward.
Sans flung open the door looking at the sight that had been left for him "papyrus i thought i taught you better, fill up the pokedex not have sex" Sans sighed. Using his eye, he lifted Mettaton and tossed him to the back. He picked Papyrus up and hung his arm over his shoulder. "aye mettaton, pal, keep your hand off my bro, 'kay?" Mettaton looked up to face Sans, who's eye was twitching. He seemed almost ready to kill someone.... "OH MY MY MY! Now Sans, calm down! We didn't go too far! We did some mouth exercises, that's all!"
Sans laughed slightly, almost maniacally. "oh really? explain paps' situation then."
Sans closed in on Mettaton, nearly suffocating him. "Uhm... Well... I-I mean, It was all foreplay. We were... n-never gonna go to far, now were we, Papy dear?" Looking at Papyrus for aid, he was met with the snore and soft breathing of the tall skeleton. "awwww. he's sleepin'. i don't care what you guys do, as long as you don't hurt my bro, ca'peche?" Mettaton nodded, still shaking from getting caught so suddenly. Sans turned and began to walk out. Suddenly, he stopped at the Lab's entrance. "oh. and don't think you're off the hook for this either, pal." With those words, Sans picked Mettaton up and flung him every which way, until finally, he was satisfied. Leaving the Lab at last, Mettaton was sprawled on the floor. Or at least, his body was.
Alphys walked in soon after. "H-Hey, Mettaton! I saw Sans and Papyrus walk by. Are... They... Al...right?" Seeing the scattered parts of Mettaton, Alphys screeched. "METTATON!"
And with that, they all lived happily never after.

The End.

'Ello Chaps! It is me, Green Michaelis, back at it again with a new story! This, was also in collaboration with my Mistress, Zoe Bean. And yes, I do understand that this isn't an anime yaoi couple, but oh to heck with it! I do find this Papy fellow quite charming, and the robot and I share something in common. Too fabulous for words! For those who aren't interested in these undertale
stories, I'll let you know that this will not be the last. The rest is up to you to read or not... If you dare. Well lads, I bid you good day. Until the next tale, beauties.