Disclaimer: I don't own any of the characters.

Unexpected Side-effect

"That's what has me so annoyed!" Sonic was pacing in Tails' workshop. The young fox watched him.

"Shadow's got his reasons, I'm sure. After everything that happened between the two of you, I doubt he'd-"

"Five months, Tails!" Sonic turned and stared at Tails. "Every month, he goes missing for three days. Not a single person can find him. You don't know what it's lie to go to bed with someone and wake up with them gone. He didn't even leave a note. When I asked him about it, all he could tell me was 'Something important'. We said we weren't going to keep secrets from each other. This counts as keeping a secret."

Tails watched as Sonic began pacing again. Under other circumstances, he'd try to help his friend. But worry over a gay lover cheating on you wasn't on his list of expertise. All he could do was hope Sonic figured something out...

"Why don't you follow him?" Sonic looked at him incredulously. "Don't give me that look. It could work. If not that, then don't give him any choice in the matter. You said it's approximately the same time every month. So just keep him home."

"It's Shadow, Tails. Shadow." He said the name slowly, as if he needed Tails to understand. "Even I can't make Shadow stay if he doesn't want to."

Sonic sat on the couch. Face in his hands, he listened to see if Tails would have any more ideas.

"Well, it's either that or live with the thought that he's cheating on you." Tails had his arms crossed. Sonic was usually confident in himself. Shadow was the only one he knew who could make Sonic question himself. For that, he both admired and hated the darker hedgehog. "I honesty still don't think he would. Not after that display he put on when he thought you were playing with him."

"I know that. I know Shadow doesn't give love easily. I'm probably being paranoid after dating Sally those few times."

Sonic stood and nodded to Tails. Leaving the workshop, he ignored Tails' questions about what he was going to do. His plan was simple. All he had to do was wait for next month.

-One month later-

Shadow woke chained to the bed. Sonic was nowhere in sight. Growl building up in his throat, he tried to move his arms. When it didn't work, the growl came out. His legs wouldn't move either. Looking at the window, Shadow began panicking. The sun was about to rise and he was still in their room. Feeling the energy building up within his body, one of his eyes closed as he tried ignoring the pain. Sonic walked in as a deep red glow engulfed his body for the sixth time that year. It was something he would never get used to. Shadow grunted as he felt his body change shape, inside and out. Pain wracked his body, though it wasn't as bad as when it had first happened. Green eyes went wide once the glow of energy faded.

"You're a... uh, nice."

Shadow lay there, panting slightly. On top of the pain, now he had to worry about what Sonic was going to do. So far all he'd done was stare. Shadow could feel the new body reacting to Sonic's gaze.

"Thought you were gay," Shadow snapped. "Stop staring at let me up."

"I'm not gay, Shadow." Sonic moved closer and leaned over the other. "I love you. What you are wouldn't make any difference. Just like you didn't care when I changed into that big hairy beast."

"You weren't big and hairy. You simply had more presence."

"It was still ugly." Sonic pouted. Sitting on Shadow's thighs, he stared down at his lover. "I mean, have you ever looked at this form in a mirror? You're gorgeous!"

"I don't like it," Shadow said. "I can't do anything in this form."

Sonic lay down on Shadow. Looking up into his red eyes, he spoke again.

"So what caused it? Some shift in the Chaos Energy? Something Eggman implanted in your body while you didn't know? Tails do something?"

"None of the above." Shadow frowned. Green eyes continued to look at him expectantly. there was no getting out of it. "Fine. Don't tell anyone. It's because of my Black Arms blood. As you know, I have Black Doom's running through my veins. As royalty, he's the only Black Arms with the ability to reproduce. That's why I have a female's body. I'm royalty by blood."

Sonic stared at him. The fact that Shadow was at least half alien was something he'd gotten used to. But it wasn't normal for random alien things to pop up out of the blue. Shadow shifted uncomfortably and averted his gaze from Sonic's. He'd feared this would drive them apart since it had first happened. Sonic claimed it wouldn't make any difference, but how could it not? He wasn't himself like this. Not at all. Looking at the wall, Shadow tried to ignore the weight on his torso. Sonic hadn't moved or said anything yet. It was almost as bad as he'd feared. A light purr caught him off guard.

"That mean I get to dominate this time?"

"No!" Shadow looked back at him with a glare. That was one of the reasons he didn't want Sonic to find out. He enjoyed fighting for who got to dominate who. As a female, he had no choice in the matter. "I never said we were going to-"

"Reproduction involves sex, Shadow." Sonic chuckled. "You know that as well as I do."

"I don't want to reproduce. I want to be left alone for the next three days until I'm back to normal. No playing around, no proving how damn weak this form is, no missions from G.U.N., and certainly no sex."

Sonic pouted. To prove his point, Shadow looked away. Sonic knew the pouting would work. It was only ever used when he really wanted something. What his body craved was what Sonic wanted. Giving in to Sonic's wishes was something Shadow didn't enjoy doing too often.

"Oh come on. That's cheating." Shadow felt Sonic sit as the blue hedgehog crossed his arms. A real pout was on his face now. The scent of arousal was obvious, and his body yearned to react to it. If Shadow said no, he might not be able to contain himself. A thought struck him then and he grinned.

"You don't want to. I understand." Sonic got off Shadow as well as the bed. "See you later."

With that said, Sonic left the room. The door was shut before Shadow had quite realized what just happened.

Damn hedgehog... Shadow growled.

Shadow lay there with nothing to do for all of five minutes before getting antsy. He could be as bad as Sonic when he had absolutely nothing to do. Shifting position yet again, Shadow tried to ignore it. If he let Sonic win after a measly five minutes, he'd never hear the end of it. Never mind how uncomfortable he got in such a position. Shadow tried to ignore everything and pretend he wasn't locked on a bed. With his normal mental state, this wouldn't be such a hard task. The way he was thinking now, all he could see when he closed his eyes was Sonic. Or rather, Sonic's dick.

"Oh, come on," Shadow said. "Being a woman now doesn't mean you have to lust after Sonic. He means more to you that. He's... The reason you are the way you are. If it wasn't for him..." Shadow blinked. "Dammit. This is why I hate being left with my thoughts." After a few minutes longer with just his thoughts, Shadow swallowed his pride and screamed. "Sonic! Get your ass up here!"

Shadow was growling by the time Sonic threw open the door.

"What the hell took you so damn long? If you're the fastest thing on Mobius, why weren't you-"

"Calm down, Shads." Sonic had that cocky grin on his face again. The one he got when he knew he was winning. Standing at the end of the bed, all he did was stare.

"Well?"

Sonic cocked his head to the side. At his angle, he could perfectly see the reaction he'd been having on Shadow's body. That moist entrance between those ebony thighs was ready for him. Nipples poked out of the white fur over the breasts. If merely thinking of him got this reaction, he couldn't wait to see what his body would get. A heavy blush decorated Shadow's tan muzzle. Pure embarrassment had replaced his usual stoic expression.

"Chaos, Shads. You make me a pervert sometimes."

A deep growl started in Shadow's throat once again. Sonic lifted his hands and backed away.

"All right, all right. You clearly don't want my help." Turning, Sonic allowed that grin to return to his face. "I can leave you there longer."

"Get back here!" Shadow's chest was heaving; he was angrier than Sonic had dared make him in a long while. "Get me off this bed."

"Sex first." Sonic turned back toward Shadow and moved toward Shadow once more. "Then I'll set you free."

His female body yearned for it. Sonic was the one he loved. Nothing but pride was keeping him from giving in. A small nod was all Sonic needed to see. Tan lips parted as Sonic's tongue made it's way through his fur to delicate skin. The thigh beneath the hedgehog's tongue twitched at the feeling. Sonic eagerly moved upward. Shadow refused to look down at the other. A pink tongue ran up into the wet opening above him. A stifled moan met his ears a his tongue made it's way into that entrance. Thighs tightened at his sides. Peach fingers dug into ebony thighs as he moved his muzzle closer. Biting just enough for Shadow to feel it pulled another twitch from the thighs he gripped.

"Don't do that," Shadow moaned. He wished the growl was still there. "No need for that..."

"Sure there is," Sonic said. "I wanna know if you taste the same."

Hips moved against his face as his tongue made it's way in and out of her. Lapping at the juices, Sonic could safely say that he enjoyed it as much as Shadow had to have been. Pants and moans spilled from Shadow's lips. Red eyes closed in both pleasure and embarrassment. Sonic always knew just how to please him. Even if it was a female's body now. Shadow felt that he ought to repay the favor.

"S-Sonic..." Another drawn out moan interrupted him. "Let me... Ahh!"

Green eyes looked up. Shadow was close. It was plain as the day. Back arching off the bed, Shadow hated himself. Losing control so completely didn't sit well with him.

As the juices flowed into Sonic's mouth, he chuckled. Shadow was like a guitar. Pull the right strings, and he'd be singing for you in no time at all. Or rather, she. With a few pants, Sonic moved away from Shadow. The heavy blush was still in place. He covered her body with his own with a sigh. It truly had been a long time since he was in this position. The fact that Shadow was female now didn't make much of a difference as far as he was concerned. Lining with each other, Sonic pushed his hips forward. Heat engulfed him as he felt Shadow's body attempt to keep him out. Clearly, Shadow still wasn't entirely sure.

"Calm down Shadow. I don't want to hurt you."

"I know that."

Shadow loosened her muscles and felt Sonic slip farther into her depths. A growl came from low in her throat again. For being the fastest thing alive, he sure was taking his time. Thrusting her own hips up against his brought Sonic fully into her. Lips clashed with one another as a quick pace was started. Neither were the type to take their time with sex. They'd proved it numerous times. A different body made no difference. It was simply a different hole to fill. Hips slammed against one another. Below them, the bed shifted and groaned. Growling was coming from both now as their pace brought their orgasms up sooner than either wanted. Luckily, they'd nearly always been insatiable with each other. Judging by Shadow's continued motions, Sonic assumed the red and black hedgehog wanted more. OF course, he had stated this transformation was for breeding purposes.

"So you want my babies?"

"Dammit Sonic," Shadow panted. "Don't bring that up now."

Sonic rubbed his hands into Shadow's chestfur. Finding the nipples, Sonic pinched them. One eye closed as a groan was pulled from Shadow.

"Stop that. You know how I get with-"

Sonic's mouth met one moments later. The fur wasn't a problem for him. He'd done it before. And he knew how much Shadow loved when things were under his chestfur. A muttered curse met twitching ears as he felt Shadow try to move his arms. Sonic chuckled. Typical of Shadow. Every time Sonic's mouth met his chest, Shadow's hands would fly right to the back of his head.

"Dammit... Sonic!"

Sonic closed his eyes and groaned as he felt Shadow's second orgasm wash over him. It was enough to send him over the edge for a second time. Panting, Shadow wished he could push the other away. None of the motions had stopped on Sonic's end.

"Just because it's the purpose of my transformation, doesn't mean you need to get me pregnant."

"How do you know if I've done that?"

"I don't." Shadow glared at the other. "And I won't know for at least three days."

"Three days? A little early, don't you think?" Sonic had a ridge raised. Shadow rolled his eyes.

"I can't change back to being a male if I'm pregnant, now can I? Somehow I doubt my body would put me through so much pain."

Sonic nodded. It made perfect sense besides the fact that it was an alien power. Tan lips parted again and Shadow threw his head back. It was getting to be too much. He loved Sonic, really did. It just wasn't a good idea for people like them to have children. Legs and arms strained against the restraints Sonic had put on him. Immortal or not, he was bound to hurt himself. That was something Sonic didn't want to happen. First released were his arms. As Shadow rubbed his wrists, Sonic leaned back and reached behind him. Red eyes went wide and Shadow moved to pull Sonic back how he had been.

"I need to release your legs." Sonic slapped the hands away. A moan came forth, cut off when Shadow bit his lower lip. A blue ridge raised. Black hips moved against his. Fumbling with the lock, Sonic was beginning to think he should've gotten off Shadow before releasing his legs. With the position he was in, it was hard to stay turned enough to see what his hands were doing. A click and Shadow's leg around his hips was the indication he'd gotten one off. Turning to the other side, he undid that as well. Shadow's other leg wrapped around his hips as well.

"Shadow, we're going to-"

"Shut up and enjoy it. Until I'm done, we're not stopping."

Rolling, Shadow pinned Sonic on the bed. For a few moments, his hips were still. Then he sat and looked down at Sonic. He'd never tried this before. But it couldn't be that hard. When his hands came to rest on Sonic's chest, Sonic gave him a smile. Lifting his hips, Shadow felt Sonic slipping from his warm depths. This was usually Sonic's job. Not his. Once the head was all that was left within him, Shadow fell heavily into Sonic's lap. Green eyes widened and a loud groan came forth. He didn't mind that Shadow had taken charge. That was how it usually worked. Lifting himself again, Shadow couldn't hold back a moan of his own. He intentionally took his time. Sonic seemed to be enjoying himself. Slamming down once more, Shadow let out a small yell. He had to admit, feeling Sonic sliding in and out was heavenly. Peach hands covered his own black ones. A sticky mess was being made, but neither of them cared. For a long while, all that mattered was each other.

-Three days later-

"How'd it go?" Tails asked.

"Shadow's pissed at me," Sonic said. "Even though it's his fault."

Tails looked confused, but it was something Sonic didn't want to get into. Especially with Tails. The door slammed open and Sonic didn't have to look to know who it was.

"I fucking hate you," Shadow growled.

When Tails saw Shadow, his eyes widened. Why Shadow was female, he wasn't sure he wanted to know. But a curious mind never stopped wondering. Before the smarter side of him could warn the other, he was speaking up.

"What happened Shadow?"

"What happened?" Shadow was yelling. He knew he shouldn't be, but it made him feel better. "That asshole got me pregnant!" An accusing finger pointed at Sonic. the blue hedgehog rolled his eyes at the claim.

"Who's idea was it to carry on? Yours, if I'm remembering right."

Shadow growled. Sonic was right and he knew it. If he wanted to blame anyone, it should be Black Doom. His blood caused the mess in the first place. In any case, he needed Sonic's help.

"G.U.N. wanted me to do something for them. I can't."

Arms crossed under the breasts, Shadow stared at Sonic.

"You know I don't... Fine." Sonic got up from his seat. "See you later Tails. Don't tell anyone, all right? Shadow doesn't want people knowing yet."

The two left the workshop. Tails stared at the door. It was one thing to hear that Shadow was half alien. But being pregnant? That was another thing altogether. tails shook his head and laughed.

"At least it wasn't Sonic. He'd make a horrible pregnant woman."

Was it fine to keep referring to Shadow as male? Or should I have changed it?