Chapter Text
To say that Sonic was curious about Shadow’s Black Arms genes was an understatement.
He knew for a fact that since Black Doom had come back a second time, something had changed Shadow’s DNA to show off more of his Black Arms genes. His tail had grown out, he had new red markings all over his body, his fangs had sharpened, and his eyes had changed to turn the scleras yellow, turn the pupils into slits, and even grow a third eye. Allegedly, he developed retractable claws, but Shadow never showed them off.
Sonic was determined to find out more.
He snuck out of the house and made sure to close the window behind him quietly so Tails didn’t wake up. He did so with ease, having done this hundreds of times before to meet Shadow for the same reason he was now: late-night racing.
Satisfied, Sonic sped off for the meadow a couple dozen miles outside Green Hills where he and Shadow always met for these races. When he arrived, he saw none other than the Ultimate Lifeform waiting for him.
“You’re late,” Shadow pointed out.
Sonic shrugged. “It took Tails some time to sleep.” He leaned in, giving Shadow a smug grin. “Why? Didja miss me too much?”
Shadow rolled his eyes. “Hardly.”
“Awww come on!” Sonic pressed his index fingers to his cheeks. “You’re really telling me you didn’t miss this old face?”
A rare grin appeared on Shadow’s face. “You said it, not me.”
Sonic pouted, ignoring the pang of sadness that echoed through his chest. “Are we gonna race or not?”
Shadow crouched into position. “You’re the one stalling.”
Sonic playfully rolled his eyes. “It’s called banter.” He got into position as well. “Loop around Green Hills, first one back wins. Count us off?”
Shadow nodded. “Three, two, o-”
Sonic took off. He heard Shadow’s air shoes racing after him. “Cheat! I didn’t finish!” Shadow yelled.
Sonic didn’t stop a laugh from punching its way out. “I left on one!” he yelled back.
Shadow caught up to him and nudged his side hard. “You were supposed to start on go.”
Sonic stumbled, but quickly regained his balance. “You’re just a sore loser.” He sent Shadow a teasing grin and stuck his tongue out for good measure.
Shadow mumbled something Sonic couldn’t hear. Before he could ask, Shadow said, “Doesn’t matter. You’ll be taking those words back soon.”
Sonic opened his mouth, but before he could say anything, he faceplanted into the ground. He felt something slither off his ankle and watched as Shadow ran ahead, his tail flicking behind him.
Sonic pushed himself to his feet and raced after him. “Hey! That’s cheating!”
Shadow laughed. Sonic almost tripped and fell again at the sound. “I thought you weren’t against it.”
Sonic huffed and pushed his legs harder. He caught up to Shadow and shoved his shoulder against his. The two continued to push and shove each other as they looped around Green Hills. They stayed neck and neck with eachother. They kept the other on their toes as they weaved through trees and jumped over ditches at the speed of sound.
Finally, the meadow came back into view. Shadow was barely ahead of him, focused on the finish line. Sonic forced himself to speed up and tackled Shadow just before his foot could cross into the clearing.
The two rolled over each other, squirming in eachother’s grasps as they fought to get over the other. Everytime Shadow was about to come out on top, Sonic would pull him down and vice versa.
Eventually, Sonic was able to wiggle out of Shadow’s grasp and ran off. “C’mon! Is that really all you got?” he taunted.
The rest of Sonic’s insults fell dead in his mouth as Shadow sprouted wings from his back. Sonic stood there, frozen as he took in the sight. Black tendrils woven together like vines spread across the sky, the bottom tips soaked in red. The bright red should’ve warned Sonic to stay away. Instead, he couldn’t help but stare and hope he could get a closer look.
In a way, that wish was granted. Shados dive-bombed into Sonic, making them roll around the meadow again. They continued to roll through them meadow until Shadow managed to effectively pin Sonic down.
The two panted as they stared at each other. Sonic was upset that he technically lost, but was more upset to see the wings gone.
After a few seconds of catching their breaths, Shadow said, “I win.”
Sonic scoffed. “You did not!”
“I got to the meadow first.”
“I crossed first!”
“Did not.”
“Did too!”
“Did not.”
Sonic rolled his eyes. “Oh bite me.”
He watched as the corner of Shadow’s mouth twitched. “I will not.”
Sonic snorted. “Dude relax, I was kidding. Plus, even if you did, I’ll live.”
This time, the corner of Shadow’s mouth curved into a frown. “I wouldn’t be so sure of that.”
It was Sonic’s turn to frown. “Whaddya mean? It’s just a bite.”
Shadow sighed and let go of Sonic so he could sit back. “Not anymore.”
Sonic briefly mourned the loss of contact as he sat up. “What are you talking about?” Shadow looked away. “Hey, it’s okay. I won’t judge you if that’s what you’re worried about.”
It was a solid minute before Shadow sighed. “You remember how my body changed because of Black Doom?”
Sonic nodded slowly, trying to conceal his excitement. “Yeah?”
“The changes you see before you aren’t the only changes that have happened to me.” Sonic watched Shadow’s tail curl around his body like it was trying to protect him. “There have been… other changes.”
“I think I saw that,” Sonic attempted to joke. Shadow gave him a flat look. “Sorry, go on?”
Shadow sighed again. “My fangs have developed two venom sacs. One set is a very deadly, fast acting venom. The other…” His ears fell back, indicating embarrassment.
Sonic scooted closer to Shadow. “Do you want to share?”
Shadow raised an eyebrow at him. “What will you do if I don’t?”
“Nothing, I promise.”
Shadow eyed him before sighing. “I know you, Sonic. It’s going to bother you if I don’t tell you.”
Sonic sputtered at the accusation, but then relented. “I still won’t do anything if you don’t want me to. I just wanna know you’ll be okay.”
Shadow looked at him again with a strange look in his eyes. It was a few seconds before he spoke again. His face turned a few shades redder as he talked. “The second set contains a powerful aphrodisiac.”
Sonic blinked. “That’s it?” Shadow narrowed his eyes at him. “Sorry! It’s just- there’s nothing to be embarrassed about for that. I was thinking it was gonna be something like a truth serum or something. I don’t know. Something way more dangerous than that.” Sonic tilted his head. “Do you at least know why?”
Shadow gave a tiny nod. “The Black Arms species is a species designed to conquer and destroy. They don’t easily feel the urge to make something. When it comes to… continuing the species, they need coaxing to get started, hence-” Shadow gestured to his teeth- “my new condition.”
Sonic nodded. “Okay, and what does that have to do with me dying?”
Shadow gave him a firm look. “I can’t control myself yet. If I bit you and accidentally injected you with venom, you could die.”
Sonic shrugged. “Sounds like you just need practice. Have you been practicing?”
Shadow pulled his legs in and crossed his arms on top of his knees. “I’ve been practicing with my food.”
Sonic frowned. “How does that work?”
“I practice trying to inject venom into my food so I can practice biting without releasing venom or aphrodisiac into it.”
“Aren’t you gonna die if you eat your venom?”
Shadow shook his head. “My body is built to neutralize it.”
Sonic nodded. He hesitated before asking his next question. “Does your body do the same for the aphrodisiac? You don’t have to answer.”
He could see Shadow weighing his options. “If my body is immune to the aphrodisiac, then that would go against the reason the Black Arms developed the trait in the first place.”
Sonic had to quickly banish non-PG thoughts from his head. “Have you tried doing it on another person?”
Shadow stared at him incredulously. “Of course not. The potential repercussions are too great. Besides, who would be a willing test subject?”
Sonic could feel his face and neck heat up. “I mean, if it’ll help you…”
Sonic could practically hear Shadow’s neck snap as he turned to face him. “You can’t be serious.”
“What? If it’ll help-”
“Did you not hear what I just told you? It’s risky-”
“C’mon Shads, Risky is my middle name.” Sonic winked at him. Shadow rolled his eyes. “Plus, think about it! If you’re only practicing on food, how will you know what the effects actually are?”
“Sonic-”
“And you have a chaos emerald on you at all times! You can heal me if things go wrong!”
Shadow huffed and looked away. Sonic watched the gears in his head turn as he thought. “What if I inject you with the wrong thing?”
“Again, you can just heal me! Quick and easy, right?”
Shadow shook his head. “Not if it’s the aphrodisiac. Chaos energy makes it worse. It enhances its effects.”
“Oh. Well then…” Sonic gathered up as much courage as he could. “Then you can… help me.”
Sonic refused to look at Shadow’s face. The next few moments were filled with tense silence. Sonic was about to force himself to laugh and say he was just kidding when Shadow said, “Okay.”
The response was so quiet, Sonic almost missed it. He whipped his head around. “Okay?”
Shadow nodded stiffly. “If it’ll help me, then I don’t see why I shouldn’t help you in return.”
Sonic grinned. “Great! Let’s get started!”
Shadow blinked. “Now?”
Sonic gulped quietly. “Uh, yeah. But only if you’re comfortable-”
Shadow cleared his throat. “It’s fine. We can do it now, I suppose.”
Sonic quickly nodded, trying to stamp down his embarrassment for being so eager. “Cool! So, uh, how do we wanna do this?”
“I bite you.” Sonic’s heart fluttered as Shadow’s eyes raked over him. “I’ll be trying to inject you with my venom first. I want to know as soon as possible if I injected the right thing into your body. The quickest way for us get results is if I bite your neck.”
Sonic nodded. He wanted to pinch himself to make sure he wasn’t dreaming, but decided against it. “Okay. What are you waiting for?” He craned his head back, showing off his neck. “Get biting.”
“Wait.” Sonic almost screamed. “We need to establish a safeword in case something goes wrong.”
Sonic nodded. “Okay, lemme think.” He rattled his brain for any ideas. Finally, he landed on one. “Branch.”
Shadow raised an eyebrow. “Branch?”
“If someone is doing something the other is uncomfortable with and isn’t stopping, we can hit eachother with a branch.”
Shadow sighed, but there was no mistaking the fondness in his eyes. The sight made Sonic’s heart flutter. “Fine. Branch is the safeword.”
Finally, Shadow crawled over so he was in front of Sonic. “Last chance to change your mind,” he warned.
“I’ll be fine,” Sonic assured him. “Unless of course, you’re too scared to-”
Sonic was cut off by Shadow clamping his jaws down on the side of his neck. He gasped and his hands flew up to Shadow’s shoulders. He could feel something cold entering his body, making him shudder. He was faintly aware of his body heating up and his breaths becoming heavier.
After what felt like too long and too short at the same time, Shadow pulled away. Blood glistened on his teeth and on his mouth. Sonic almost moaned at the sight of it.
“How do you feel?” Shadow asked.
Sonic nodded, but then realized that told Shadow nothing. “Good,” he managed to get out.
Shadow’s eyebrows creased. “Good? What do you mean?”
Sonic thought about it for a moment. “I mean, I feel really warm? But it doesn’t feel bad. And my head’s all floaty and-”
He was cut off by the sudden intense feeling of emptiness. His pussy throbbed around nothing and he could feel himself getting wet.
“I don’t think that was venom,” Sonic revealed.
Shadow’s eyes widened. He tossed his head back and groaned. “Fuck.”
That didn’t help Sonic’s condition. In fact, it just made it worse. Hearing Shadow talk like that made him want to climb onto his lap and start grinding on him. Sonic swallowed his saliva and managed to pant, “So. You gonna help me?”
Shadow eyed him warily. “Are you sure?”
Sonic couldn’t find it in him to stop his hips from bucking up to find some sort of friction. “Yes. Chaos, yes. Please Shadow-”
“Safeword?”
“Branch! Fuck, please-”
Shadow cut him off by kissing him hard. Their teeth clacked together from the impact, but Sonic didn’t care. His head spun from the contact and he let out a low moan. He was dimly aware of the fact that he was taking off his gloves and weaving his bare paws into Shadow’s quills.
Shadow took off his own gloves and pulled him closer. He kissed along Sonic’s jaw and neck before reaching up and tugging his quills. Sonic gave a heady moan as Shadow continued to kiss him up and down.
Sonic crawled into Shadow’s lap and sat down on his crotch. He rubbed his sex desperately against the growing hardness underneath him. His clit twitched at the constant contact, but he wanted more. Chaos above, he wanted so much more.
Sonic felt Shadow lower him so he was laying down. He felt him leave a trail of kisses down his torso, pausing to leave a string of them along each top surgery scar. Sonic pushed his body up to meet Shadow’s lips, growing more eager as he came closer to where he needed contact the most.
Just before Shadow’s lips trailed to his leaking slit, he moved back up and pressed a kiss to one of Sonic’s nipples. He gasped at the sensation and arched his back. Because he was on testosterone, his nipples weren’t as sensitive. Now though, it felt like he’d come into contact with a livewire.
Moans tumbled out of Sonic’s mouth as Shadow continued to suck away. He gasped again when he felt Shadow lightly pinch his other nipple between his fingers and start rolling it between them.
“Fuck, Shadow,” Sonic moaned.
Shadow didn’t respond, instead switching pecs so he was sucking the one he was previously playing with and fingering the other. Sonic wrapped his legs around his waist and began rutting against his crotch.
“Please Shads,” Sonic begged. “I need more. Shads-”
Shadow paused his sucking, but left his lips against Sonic’s chest. A shiver went up his spine as Shadow’s voice rumbled out. “Where do you need me?”
“Lower please.”
Shadow resumed kissing a trail down his torso. After what felt like centuries, he finally made it to where Sonic needed him most. He could feel that his seam had opened, exposing a red, throbbing clit and hole leaking with slick.
Shadow traced a finger through his seam, gathering slick on the tip of his finger. He raised his finger, showing off a black hand with a red stripe going down the middle and ring finger. He stuck his slickened finger in his mouth and sucked it. Sonic’s head fell back as he let out another long moan.
Shadow laid down, nestling his head between Sonic’s legs. He placed Sonic’s legs on his shoulders and pulled him forward by his hips. Shadow’s eyes met Sonic’s as he pressed a soft kiss to his small dick.
That action alone tipped Sonic over the edge. His back bowed as he cried out, slick flooding out from his pussy. He panted as Shadow pet his thigh gently.
“How are you feeling?” Shadow asked. “Are the effects going away?”
Sonic shook his head. “More,” he managed to gasp. “I need more.”
“I’ll give you more, don’t worry.”
Shadow returned his lips to Sonic’s clit. He engulfed it and began sucking and flicking his tongue against it. Sonic practically sobbed at the sensation. He grabbed the back of Shadow’s head and humped it desperately as he chased another climax.
As his next climax rapidly approached, Shadow snaked his arm out from around one of Sonic’s legs and ran two of his fingers through his pussy, collecting more slick. Once he seemed satisfied, he slowly pushed two fingers into Sonic’s gaping hole. Sonic’s hips bucked forward, helping Shadow’s fingers inside of him.
Shadow swirled his tongue around Sonic’s clit as he pumped his fingers in and out of him. Sonic continued to grind against him, seeking out stimulation. His eyes flew open with a loud gasp as Shadow hit his g-spot.
Shadow picked up on his reaction and aimed his fingers to hit that spot every single time. Sonic couldn’t stop moaning out yeses, pleases, harders, and mores as Shadow continued to abuse that spot. It wasn’t long before Sonic squirted all over his fingers.
Shadow slowly pulled out of his vagina, making Sonic whine at the overstimulation and emptiness. Much to his delight, however, he felt Shadow’s tongue lap up his slick and slide into his cunt.
Shadow wasted no time. As soon as he found Sonic’s g-spot again, the relentlessly lapped against it. Sonic cried out as he was worked through his overstimulation towards another orgasm.
Shadow abruptly pulled out of Sonic. He flinched at the sudden emptiness and was about to start begging for him to come back when Shadow pressed his thumb against his lips. “Open,” he commanded.
Sonic opened his mouth and Shadow stuck his thumb in. “Suck.” Sonic swirled his tongue around the digit. Shadow grinned. “Good boy.”
Sonic moaned around his finger as his hips twitched up. His pussy throbbed and leaked more slick. Shadow raised an eyebrow. “Do you like it when I call you a good boy?” Sonic nodded rapidly.
Shadow took his thumb out of Sonic’s mouth a pressed a searing kiss to his lips. “Then you better behave.”
Sonic moaned again as Shadow moved back to his previous position. His tongue entered his hole again, but this time, Shadow ran his thumb around Sonic’s nub. “Fuck, Shadow, please,” he gasped.
Shadow didn’t respond. Instead, he kept tongue-fucking Sonic. He writhed at the feeling until Shadow held him down with his free arm. It concentrated the sensations along Sonic’s cunt as he was pushed to cum again.
He felt Shadow slide out of his hole. “How do you feel?” he asked.
To be honest? Still too horny. His cunt spasmed and throbbed, searching for more stimulation.
“Your dick,” Sonic gasped. “I need you to fuck me Shadow.”
“Are you-?”
“Please Shadow!”
Shadow studied his expression before nodding. “Okay, if that’s what you want.”
He sat up, revealing his dick. It had come out of its protective pouch some time ago. Sonic practically drooled at the sight. Shadow’s dick was a tentacle, starting small and tapered at the end, but gradually thickened the closer it got to Shadow’s body. All along the dick were ridges. The tentacle flicked around, seeking sensation.
Sonic got up and crawled to Shadow. He slowly took his dick in his hand, slid the tip into his mouth, and sucked on it. Shadow tossed his head back, moaning as he placed his hand on Sonic’s head.
Sonic hollowed out his cheeks and bobbed his head back and forth. He ran his hand along the length, sucking desperately. He used his free hand to move Shadow’s hips towards and away from him. Shadow got the message and began fucking into Sonic’s mouth. Sonic drooled and moaned as Shadow’s cock hit the back of his throat.
“Shit, Sonic, I’m going to cum soon,” Shadow groaned out. “One tap for in, two for out.”
Sonic tapped once against Shadow’s thigh and moved his head faster to meet Shadow’s pace. His hand traveled from Shadow’s thigh and found his small dick. He wrapped his fingers around it and began pumping it in tandem with Shadow’s thrusts.
Shadow groaned as he came inside Sonic’s mouth. Sonic happily swallowed the spend up, humping against his hand. When Shadow slowed to a stop, he pulled out of Sonic’s mouth and kissed him hard.
“Do you still want me to fuck you?” Shadow asked between kisses.
Sonic gave him a shaky nod. Shadow laid him down again and positioned himself between Sonic’s legs. Sonic felt his dick slither across his slit before burying itself inside. Sonic keened as Shadow slowly rocked himself in and out of his cunt.
When Shadow bottomed out, Sonic felt like he could barely breathe. He looked down and saw his lower stomach move in time with Shadow’s dick squirming inside of him. His hips twitched and insides pulsed at the feeling.
“I’m going to start moving now,” Shadow warned.
Sonic nodded. Shadow began moving his hips back and forth, the ribbing along his cock rubbing the walls of Sonic’s pussy. Sonic couldn’t stop moaning. He knew that from this point forward, he’d been ruined. Everytime he was going to jack off, all he was going to think about was Shadow’s dick.
“Shads, talk to me,” he panted.
Shadow slowed. “Why?”
“Just wanna hear your voice.”
“Hm.” Shadow picked up his pace again. “Do you like the sound of my voice?” Sonic nodded eagerly.
Above him, Shadow chuckled. “Is that why you’re always seeking me out? Because you want to hear me talk? All I ever do is insult you. Unless you like that too?” Sonic whined. Shadow’s grin grew. “Do you like it when I call you an idiot?” Sonic’s hips spasmed at that. “And if I call you other things? What if I called you a bitch?”
Sonic tossed his head back with a low moan. He felt Shadow pistoning his hips faster. “Is that what you like? Do you get off everytime you go back home from our races? You need me to insult you to get off? Or my attention alone?” Sonic nodded weakly.
Shadow laughed at Sonic’s embarrassment, thrusting harder into him. “How naughty. How would your friends react if they knew you had such a slutty mind?”
Sonic could only moan. The words made him dizzy with arousal. He rocked his hips back and forth to meet Shadow’s, squeezing his muscles to feel his dick better.
Shadow continued to rut into him, switching from insults to praises. The constant switch up made Sonic’s head spin in way that felt oh so delightful.
As Shadow began to fuck away, Sonic noticed an odd sensation. He could feel the tip of Shadow’s cock hitting something deep inside him, but it also felt like it was opening.
When he realized what was happening, Sonic couldn’t help but beg. “Shadow, keep fucking me. Fuck, you’re fucking my cervix open. Don’t stop, it feels so good-”
In the middle of his begging, he felt the tip of Shadow’s dick slide deeper inside him, surpassing that barrier. The feeling was enough to make Sonic cry out and squirt again.
He felt Shadow begin to slow down, which annoyed him. Sonic wrapped his legs around Shadow and gyrated his hips to encourage him to keep going. “Don’t stop,” he demanded. “Keep fucking me.”
Shadow’s eyes widened before he began slamming his hips against Sonic’s. His body bounced from the force of Shadow’s thrusts, forcing himself deeper inside Sonic. He didn’t know how being so deep felt so good, but Sonic didn’t want him to stop.
“Just can’t get enough, can you?” Shadow huffed. Sonic shook his head. “I’ll cum in you at this rate.” Sonic nodded. “What, you want my cum? You want me to fill you up until you’re fat with my hoglets?”
Sonic nodded quickly. Shadow continued to hammer away at his insides, reducing Sonic’s mind to mush. All he could think about was how good this felt and how he didn’t want it to stop.
Shadow’s steady thrusts soon grew uncoordinated and desperate. “Last chance Sonic. You wanna take my cum like a good boy?”
Sonic nodded again. Shadow thrust hard a few more times before moaning into Sonic’s shoulder. Somehow, Sonic could feel Shadow’s cum filling his womb. Sonic screamed in ecstasy as his final orgasm took him and whited out his vision.
When Sonic came to, he was lying in the grass with Shadow hovering above him, concern written on his face. “Sonic?” he asked.
“Hey,” Sonic replied, his throat hoarse. “How long was I out?” He didn’t feel Shadow’s dick inside him, but he could feel cum dripping out of his hole.
“About a minute.” Ah, Sonic was right. “How do you feel?”
Sonic took a second to check himself. “Better,” he concluded. “I think the aphrodisiac wore off.”
Shadow nodded. “You should get emergency contraceptives as soon as possible.”
“I’m good. I have an implant, so no pregnancy for me.”
Shadow nodded again. Sonic took a deep breath and looked around. “Sooo… you wanna try again next week?”