Peter had to admit that the first time he had seen Loki’s true form, he had been frightened. Loki had been furious during the fight with Thanos’ army and seemed to slip without realizing it until Thor had pointed it out afterwards. Even though he had been scared, Peter couldn’t help but want to see more. There was a beauty to Loki when he was completely lost in himself like that and Peter wanted that for himself.
The second time Peter saw Loki’s true form was an accident. Loki slipped up during an argument with Thor and showed himself. When Thor recoiled away, looking disgusted, Peter started to understand Loki’s hesitance to show him more willingly. The thought enraged him. He stepped between them, one arm protectively in front of Loki, and he couldn’t remember what he had said to Thor, only that it must have been loud, since every Avenger in the vicinity was on them in moments, ushering Thor away from Peter while Peter hugged Loki around the waist, whispering “I’m sorry” over and over into his cool, blue skin until the room cleared and they were left alone in the quiet of one of the tower’s living rooms.
The third time was when Loki gave in. Peter asked, as he tended to do when they were alone, and Loki decided for once not to turn him down. Peter wasn’t sure what had gone through Loki’s mind when he decided to let the illusion fall, but he was grateful he had. All at once, Loki towered over him. His eyes were closed, face turned away like he was sure that Peter would tell him to hide it again any moment. Instead, Peter reached forward to run a hand over the raised markings on his body. Loki shivered, opening his eyes and watching as Peter continued to trace over the marks where he could see them around Loki’s clothing.
“God, you’re beautiful,” Peter sighed. “And huge. ”
Loki scoffed, a sneer of disgust crossing his face. “I am a runt. Useless. Unwanted by anyone.”
“That’s not true.” Peter shook his head. “I want you.” He blushed when he realized the words that had come out of his mouth.
“Strange child,” Loki looked away, almost like he was embarrassed.
“Not a child,” Peter glared.
Loki tapped his nose with one finger. “The oldest human to ever exist was a mere baby by comparison to us.”
“Show me more.” It was a demand as much as a plea.
Loki obliged, unclasping his tunic to let it fall open and reveal the expanse of his blue chest, ridged with even more raised markings and still more white scars. Peter sucked in a breath, trying to keep his composure. Normally, he and Loki were not so different in size, but now Loki towered over him, leaving his eyes level with that beautiful chest. It made something twitch deep in his gut.
“You’re so big,” Peter mumbled, spreading his hand wide and still not covering even half of Loki’s stomach.
“Maybe you’re just small, spiderling,” Loki teased.
“Maybe,” Peter hummed. “I like it.”
“You like it?”
“You could just… Do whatever you wanted to me.”
“I could always do that,” Loki’s brow furrowed, like he was starting to catch on to what Peter was getting at. His hand cupped Peter’s cheek, tilting his face up to look at him.
Peter whined. He thought Loki must know what he was getting at, he just wanted to make him say it. “Please?”
“Use me,” Peter’s voice was barely a whisper.
Loki moved both hands to Peter’s hips and lifted him easily. Peter let his legs wrap around Loki’s waist, barely able to cross his ankles behind his back. His hands clasped behind Loki’s neck, anchoring them together. When Loki leaned down to press their mouths together, Peter rolled his hips against his stomach, searching for any friction he could get. Loki purred into his mouth, or at least made a sound that Peter could only describe as purring, and carried him to the couch where he sat down with Peter on his lap. Something about their position made Peter feel even smaller and weaker. It had him panting with want before Loki had laid a hand on him.
"Get these off," Loki growled, tugging at the waist of Peter's pants.
Peter stood up to yank them off, along with his boxers, before immediately straddling Loki's lap again. With a casual wave of his hand, Loki's pants disappeared, leaving their bare flesh pressed against each other.
“Cheater,” Peter huffed softly.
Loki smirked at him.
While Peter had never considered himself small, his cock was dwarfed by Loki's where they brushed against each other. Peter leaned in, kissing Loki deeply and in the process trapping their cocks between them so that he could rock his hips against Loki's. Loki's icy hands gripped his hips, hard enough that Peter hoped there would be enormous bruises where his hands were. He gasped into Loki's mouth, biting and sucking desperately at his cool lips.
Before Peter could stop himself, he was trembling and coming across both their stomachs. Loki growled deeply, then tossed Peter down onto the floor. The impact knocked the wind out of him and Loki was on top of him in a second. His fingers were slick when they pushed into Peter, cold and thick. His legs tried to close from the shock of it, but one of Loki’s huge hands pinned one of his thighs to the floor.
His fingers were removed almost as quickly as they had been thrust in. The blunt head of Loki’s cock quickly replaced them. Though the stretch burned, the icy feeling of Loki inside him had Peter hard again and shaking before he had even made it all the way inside. Loki’s hands gripped his thighs, keeping them spread as wide as they possibly could be. When Loki leaned over him, Peter let his hands drag through his hair.
“Nngh, you’re so pretty,” Peter choked out.
Loki released Peter’s thighs and dropped his head down to mouth at his neck as his thrusts started to get shorter and sharper. Peter wrapped his legs around Loki’s back, using whatever strength he could find to try and stop Loki from pulling out. He wanted to feel it deep inside him.
“Peter,” Loki whimpered as he started to come inside him.
There was a sudden stretching inside him that made Peter’s spine arch up off the floor and set off his own second orgasm. The thickness, however, didn’t go away as they laid on the floor panting. Every so often, Peter could feel Loki’s cock twitch inside him and pump more come inside him. It made him shudder, which in turn made Loki gasp into his neck. When he stole a glance down, Peter could see that his stomach was starting to bulge out.
“How long,” Peter struggled to pant out. “How long does this last?”
Loki shook his head. “I don’t know.”
Loki lifted Peter gently off the floor, jostling the fluid inside him and making him whimper. Peter let himself be carried through his own room in the tower to the attached bathroom, where Loki sat them down in the bathtub, knees bent so that Peter could lean back against them. Peter wasn’t sure how long they were tied together, only that by the time Loki had softened enough to be able to pull out, his stomach was bloated and sore from being stretched, but he felt full and happy and never wanted to give the feeling up. When Loki did slip from him, he blushed and gasped at the feeling of come rushing out of him. He shut his eyes against watching his stomach flatten.
“Shh,” Loki pet down his face. “You look so pretty when you’re a mess.”
When Peter’s was able to open his eyes and look at Loki again, he was back to looking like his usual self with a very satisfied smirk on his face.
“Maybe we should do this more often,” Loki teased. He added, voice dropping to a harsh whisper in Peter’s ear: “If your tiny body can handle it.”