A/N: This is the only Royai week prompt that grabbed me. Enjoy!

Roy Mustang was practising alchemy with Grumman when they hit an impasse.

"You should go check the notes," Grumman said and Roy nodded, though he inhaled sharply as he walked away. This was getting more and more difficult. Roy tried to steady himself as he walked up the stairs and knocked on Riza's door.

"One minute!" she said, and then opened the door shirtless, in her jeans with a towel pressed against her chest. At first, Roy had only been interested in the alchemy, able to focus on nothing but the symbols on her back. But as time went on, he became acutely aware of the fact there was a naked young woman standing in front of him. He couldn't stop staring at her sculpted figure, her round breasts barely concealed by the towel and her adorable, impish face. Sometimes he wondered if she dreamed of him too. Her breath often quickened as he studied her tattoos, and the light hair on her back seemed to stand on end. But maybe it was just his imagination. Roy didn't want to take advantage of the situation Riza was so unfortunately in, having been tattooed as a child by her unstable father.

"The nubile daughter, what a prize," Grumman had joked once, when he'd seen Roy make a wayward glance in Riza's direction. He'd taken this as permission, but he was still cautious. Roy tried to hide the erections that had started growing every time he went into Riza's room. He started taking a minute or two to cool down in the bathroom before he went back to Grumman, thinking about his mother soaking her callouses, or Grumman and his lady friend who Roy thought might actually be a gentleman friend in lady's clothing, anything to get his thoughts off of Riza. But Roy thought Grumman still noticed how flustered he was every time he returned. Grumman seemed amused. Roy could only hope that Riza was too naive to notice.

Roy tried to calm himself as he studied Riza's tattoos yet again. He heard her breath quicken, but tried to ignore it. Reading some symbols, he used his hand to trace a line on her back without thinking. She let out a small sound and then, as if it had taken her a moment to build up the courage, pulled his hands to touch her breasts, the towel fluttering down towards the ground. Roy caressed them, pulling her closer and placed a kiss on the back of her neck. His erection raged, pressed against her bottom.

Riza broke free from his arms, and turned around and kissed him hard. He let out a low moan as her hands ran down his back and traced the waist of his pants. He kissed back harder, letting his hands run through her golden hair. Then she pulled away.

"You should go," she said. Roy looked at her, wondering if he had done something wrong. She seemed to sense this.

"That's enough for now," she tried to explain, looking overwhelmed. Roy nodded, realizing she must not have much experience, and was probably worried about her grandfather walking in.

"Well, I'm always here if you need me," Roy responded, and she gave him a mischievous smile that indicated that she was planning to take him up on that. He shivered at the thought.

Afterwards, Roy sat fully clothed on the bathroom toilet, breathing heavily and trying to calm himself down. He pictured the Fuhrer and his Generals having an orgy, and then Dr. Knox having sex with cadavers, but it didn't help much. This was going to be a problem.

A few days later, after dinner, Roy was relaxing in his room when Riza walked in. She explained that it was time for Grumman to listen to his favorite radio show, and he was unlikely to disturb them. Roy was glad that Riza was clever as well as being beautiful. She gazed torridly into his eyes as she slowly removed her shirt and bra, and then whispered,

"No hands below the waist, okay?"

Roy nodded. He would have agreed to anything to run his hands along her silken skin, to taste her velvet lips. Desire stirred within him as she walked towards him, her breasts bouncing slightly and sat in his lap. He thought he might die from longing. Eagerly, he caressed her chest, pinching her nipples slightly, and she let out a small moan that awakened something in him. He knew exactly what he wanted to do to her. He wanted to peel every piece of clothing off her body, one by one, and explore the underlying skin, explaining every unfamiliar sensation. Then he wanted to pull her legs apart and awaken her body. Roy unconsciously gripped Riza harder, and she kissed back fervently. Heat rose through him as she rocked back and forth in his lap. Just as he was considering laying her on her back, the ending theme of Grumman's show boomed loudly. Riza quickly dressed and ran back to her room, leaving Roy with an erection that thankfully he had time to take care of.

Riza continued visiting Roy's room a couple of days a week. While she still held him to the same rules: just her shirt off, only touching above the waist, after she left he always felt like he had been visited by the Gods. But Roy also thought she was getting close to being ready for more. She'd started pushing him down onto the bed and pressing her pelvis hard against his erection until she was breathless. Roy found this unbearably stimulating, often gasping involuntarily before Riza muffled him with a kiss.

He started off by asking to remove his shirt. It wasn't a big move, but she agreed to it. He could tell it made her even more aroused. Her eyes smoldered more intensely, her breath was more ragged and she seemed to lose all focus, indiscriminately grabbing him and rubbing herself against his body, groaning in frustration. Beads of sweat ran down her face as she writhed desperately. She ground against him so hard that he started trembling, dangerously close to the edge.

"You need to stop that," he gasped. Riza looked up unsteadily, her breath heavy.

"But I need it," she wailed, slamming her fists on his chest, "I really need it."

Roy smiled with amusement, before kissing her neck and whispering,

"Can I try something?"

Riza nodded. She looked so captivating with her face flushed, her sweaty hair in disarray and her lips red from kissing. Roy gently flipped her over onto her back and unzipped her pants, then ran one hand over the front of her underwear. She took in a small breath, and then released it as he slowly stroked her mound. Her face wore an expression of astonished pleasure. Roy kept working as she squeezed her eyes shut and emitted slight moans, and then cried out, wetness soaking her underwear. He traced circles until she pulsated and screamed. Then he pulled her into his arms and kissed her.

"Was that what you needed?" he whispered after she'd calmed down a bit. She nodded, and kissed him harder.

Now Riza was down to her underwear, as Roy touched her shirtless, but she still loved grinding against him. He knew it was a matter of time before he would have an accident, and then he did. She started rubbing her crotch against him, with an adorable toss of her head, and was so rapt by the time he told her to stop that she didn't seem to notice. He gave off a guttural groan and exploded, sending spurt after spurt into his pants. As he sat up, he saw wet patches soaking through.

"Do you know what you did?" Roy asked Riza. She nodded gravely.

"Well, if you want to do it again, you need to take my pants off," he told her sternly. He didn't think there was a single thing that Riza could do that would annoy him, but soiling his stylish pants was getting close. She left, and he peeled them off, wondering if they would ever be clean. Worst of all, he realized that it was Grumman who always took the household's clothing to the laundry. He supposed he could just hide the pants under his bed for months until he went home.

The next time Riza visited Roy, she stripped down to her underwear and then pulled his pants down, hard. He was surprised by her aggressiveness, but he didn't resist. She removed his boxers at top speed too. She motioned for him to sit down, and he did, then she sat down at his feet beside the bed. Riza inspected his member curiously, moving her head to each side, and then pulling his legs apart to get a better view. He wasn't even hard yet, but she started stroking him softly, changing this. When he reached full mast, she plunged his whole cock into her mouth.
Roy groaned loudly, wondering what deity he had pleased to deserve this. Her mouth was slick and her tongue fluttered thrillingly at the tip of his shaft. Riza's short blond hair fell everywhere as she moved more quickly. Suddenly, she started sucking and he lost all sense of his surroundings. Years could have passed, he could have been screaming at the top of his lungs for all he knew. The only things that were real were her mouth and his pleasure and the sheets clenched forcefully in his hands. He wanted to warn her, but his climax was so intense, so sudden, that he couldn't speak. She tried to swallow, but his seed dripped out of her mouth and onto her chest. Roy lifted her up onto his lap, and wiped her off with a sheet.

"Where did you learn to do that?" he asked in amazement.

"From a book," Riza said softly.

"What type of book?" Roy asked. Riza turned red in embarrassment and didn't answer. He put his hand between her legs and stroked her softly, trying to lower her inhibitions. Once her breath quickened, he asked again,

"Tell me about the book."

"It's a book of dirty stories," she gasped between breaths, "I found it in Grandpa's stuff."

Roy rubbed Riza harder and she whimpered.

"I approve of this," he said warmly, "And if there's anything else you want to try, just let me know."

She nodded as she fell apart, moaning and clutching onto him.

A few weeks later, Grumman announced he was going on a trip. He claimed it was military business, but Roy suspected he was visiting his ambiguously-gendered personal friend. But Roy didn't ask too many questions, because it would be the first time he and Riza would be left alone. That night, she came into his room and asked if she could sleep in his bed.

"I don't want to impose," she said. Roy nearly laughed out loud. He would have given her his car, his mother's house, the balance of his bank account. That was how good she made him feel. He was certainly willing to share his bed. He pulled back the blankets and told her there was no way she could ever impose on him.

After Roy turned out the lights, they embraced each other. It was as comforting as it was arousing. They were so close it was unreal. Except for that annoying pair of underpants he couldn't entice off her body. He put his fingers in the waistband and tugged on them, but she whispered,

"Don't" into his ear. He moved his hands up her torso with disappointment. This was the stuff that dreams were made of. He wanted to taste her.

"I want to go on a picnic tomorrow," Riza told Roy. He nodded his head in agreement. The last few days had been extraordinary. It wasn't just the petting, but cooking together, the long conversations, sitting in each other's presence while he studied alchemy and she read magazines. He thought he wanted to marry her. If only every day of his life could be like this.

They made a basket of sandwiches, laughing together flirtatiously as they chopped and wrapped. Then they walked out to a lovely meadow that Riza suggested. Roy couldn't stop watching her as she walked. She was wearing a short sundress, and every so often she stumbled, causing it to bounce upwards, revealing an inch of her covered rear. He didn't think she realized what an effect such clothing had on him. Roy decided that as soon as they got home, he was going to lift her dress up, press her against a wall and do disgusting things to her. He hoped the gods had been listening to his prayers and she would relinquish that underwear.

Riza laid down a blanket under a tree, and they sat and ate the sandwiches, feeding small pieces to each other. Then Roy put his arms around Riza and they watched the trees sway in the distance for a long time. It was so serene, with the breeze in their faces and the smell of grass below them. Roy considered telling Riza he loved her, but he didn't want to risk ruining the moment.

She turned around and kissed him. At first, it was chaste and romantic, but after a while her kiss got harder and harder. Soon, she tugged the skirt of her dress above her waist, and lay down, pulling Roy with her. Her hands circled around his waistband and pulled at his belt.

"I don't think we should do this here," he whispered, "Someone might see."

"It was in the book," she insisted, "You said we could do stuff from the book."

Roy looked at Riza in disbelief. He hadn't intended to write her a blank check. He looked around, wondering if they were visible. They were under a tree in a farmer's field, and the grass was quite high, but he was still worried that someone might walk by on a nearby path. Then he saw Riza remove her underwear.

Roy couldn't resist. Returning to his place on top of her, he kissed her mouth and then her neck. Continuing downwards, he reached her belly button, and then ventured lower and lower. She was delectable, she was lucious. He ran his tongue across her folds, over and over, listening as her moans intensified.

"Roy," he heard Riza say, interrupting his bliss. She pulled him upwards so they were face to face. Her arms closed tightly around his waist and she kissed him harshly. Turning her head, she pressed her lips beside his ear, then with mild embarrassment whispered,

"I want you to fuck me."

Roy looked at her in surprise. He'd expected it would be a long time before she lifted this final bar.

"Are you sure?" he asked. She nodded. He slowly unbuckled his pants and pulled down his boxers, and then put one hand between her legs and caressed her lightly.

"Please," she whispered, "Do it now."

He pulled her legs apart and lowered himself into her slowly. Riza turned her head and hissed at first, slamming her eyes shut, but then let out a satisfied sigh. She was so unbearably tight and Roy had wanted her for so long that he could barely contain himself. He let out a loud wail.

"Riza," he breathed into her ear as he started pumping slowly, "You are everything."

Roy tried to be gentle, though it was hard to fight the urge to take her as hard as he could. Holding back was almost painful. Every thrust sent him to new heights, making him moan louder.

"More," he heard Riza gasp. He barely needed an invitation. He plunged down harder and harder, moving his hand between her legs to give her more stimulation. She started to whimper, and he stroked more forcefully, moving his head downwards to suck on her nipples.

"Please, Roy," she cried, "Please, please."

He gave her one last solid thrust, and he felt her convulse, closing in on him. It sent him over the edge.

"I love you," he said to Riza without thinking, feeling like he'd traveled to another world.

"I love you too," she whispered back, perspiration dripping down her forehead. He held her for a long time, the sky above them, listening to the breeze.

When they got up, Roy saw they'd soiled the blanket badly. Riza had really bled a lot, and there were his fluids too. He decided that they would need to dispose of it. While Grumman didn't seem opposed to them having a relationship, Roy worried he might change his mind if he saw something that so clearly indicated what had gone down. He figured they should just throw the blanket in a creek somewhere and take no chances of him ever finding it.

"But I want to keep it!" Riza insisted. Roy looked at her in surprise. "You know," she went on, "For when I touch myself."

Roy's eyes widened, but he decided it wasn't worth arguing about.

"Just make sure you keep it somewhere your grandfather will never find it, alright?" he said uneasily.

Riza wrapped the blanket around her body, putting it over one shoulder, and under the arm on the other side, and kept it like that as they walked home. She pressed her cheek against it every so often, and once she accidentally brushed her arm against a wet spot, leaving a smear. Immediately, she raised her arm and licked it off.

Roy realized that Riza had Grumman's eyes, and he knew that look. It was the same one that Grumman wore when he sorted through his collection of used pantyhose, or added a new photo to his albums of women in diapers, or any of other stuff Roy tried to avoid noticing he did. Roy had read somewhere that sexual deviance was hereditary. He looked at Riza and wondered if he was looking at a young pervert.

The next few days were madness. Roy and Riza couldn't keep their hands off of each other. They spent hours in the bedroom, but also the kitchen, the bathroom, the living room, the attic, the garage and the alchemy study. Once they even did the deed on the dining room table. Roy walked around nervously with a rag every so often, making sure every surface was clean. He didn't want to risk Grumman finding anything to tease him about.

Roy's underwear had been slowly disappearing ever since he'd moved in with Grumman and Riza. He'd started off with fourteen pairs, but now he was down to nine. Roy had assumed the laundry was sloppy, as Grumman was always trying to shave cents off of costs like that. But as he watched Riza sitting peacefully, listening to the radio, wrapped in the soiled blanket from their picnic, he had another idea.

"Riza," he asked, nestling next to her, lightly kissing her cheek, "Did you take my underwear?"

She paused for a moment.

"Maybe," she said, blushing.

"Can I have it back?" he went on, adding flirtatiously, in a husky tone, "Now that you can touch a lot more than my underwear, maybe you don't want it anymore."

Riza shrugged her shoulders.

"I still like it," she said impishly.

"Can you give me at least a few pairs back?" Roy persisted, "I'm worried I'll run out"

"You should wear my underwear," she said coquettishly, "Then you'll be able to smell me a bit and be a bit turned on, but no one else will be able to tell, even if they see you in public. It would be like a sexy secret."

Riza looked enthralled by the prospect.

"I don't think that's a good idea," Roy said, shaking his head a bit.

"How about I buy you some new underwear as a gift?" Riza asked.

"Sure," he said, and then added sternly, "Normal underwear. And you have to promise not to take it."

Roy carried several bags into the house and Riza trailed behind him. They'd gone to the grocery store and Riza had worn another seductive dress. As soon as the groceries were stored away, he caught her in his arms and ran his hands underneath the skirt.

"Wow," said Riza, "You sure like these dresses."

Looking at her, he decided he'd had enough of her games.

"You," he spat, gripping her ass, "Are a little nymph. You pretend to be so innocent, but then stand there, gyrating, knowing you're driving me wild."

Riza gave him a sweet look, like she had no idea what he was talking about. Even as she spoke, she shifted a bit, moving her skirt and giving him a glimpse of her underwear. He picked her up and carried her up the stairs, ignoring her protests and lay her across his bed. Opening a drawer, he pulled out two belts, and used one to fasten her arms to the headboard, and the other to hold her legs together at the ankles. Riza looked stunned, but also excited.

"You," he growled, his face hanging inches away from Riza's, "Are going to confess."

Roy also had a confession, though he wasn't planning to make it yet. He had found Riza's erotic book and read all the way through, noting which parts had bookmarks and dog ears, and which pages were so wrinkled she'd clearly read them over and over. Roy had a strong suspicion that this interrogation would drive her wild.

"What are you going to do to me?" she asked eagerly.

"Nothing," Roy said, "Not until you tell me."

He slowly undressed as she watched with wide eyes, and then stroked himself as she stared ardently. Riza struggled against the restraints, which seemed to excite her further. Sweat was beading on her forehead and her mouth was open, panting. Straddling her legs, Roy whispered questions into her ear, denying her until he got answers.

"I saw you get out of the shower by mistake," she wailed at one point, "And then I couldn't stop thinking about you."

"Was it really a mistake?" Roy demanded.

"It was the first time," she squealed.

Roy rewarded that with a kiss.

"You smell so good," she groaned later, "I just wanted your boxers so I could smell them."

"What did you do while you smelled them?" he demanded.

"I touched myself," she cried, looking downwards, a pink blush spreading across her face.

"Like this?" Roy asked, pulling down her soaked underwear, and pressing his fingers into the moistness.

She inhaled sharply as she nodded.

"I just wanted my first time to be special," Riza moaned after another question, "And I just wanted you so badly."

"What did you want?" he asked again, and again, until she gasped in broken words,

"I wanted your cock, I wanted your cock to break me open!"

"Do you want it now?" he asked softly. She nodded desperately. He removed the belt from her legs, pushing them open and went in, forcing Riza against the headboard. She opened her mouth and screamed.

"Did you like that?" Roy asked later, unbuckling her arms. She didn't speak.

"Holy fuck," she said when she caught her breath, "I loved it."

Roy laughed.

"No more pretending," he whispered into her ear, "You know exactly what you do to me."

Grumman returned the next day.

"Did you make much progress on Flame Alchemy?" he asked. Roy shook his head and said without thinking,

"I was a bit busy."

Grumman raised his eyebrows.

"I mean, I had to do all the cooking, and get the groceries and sort the laundry," Roy invented.

"I'm sure," said Grumman.