A/N: Hey, guys! I promised I wouldn't do this, but I couldn't help it. This story is one that came to me the other day, so I want to see if people are more interested in my baby that I've been working on for half my life, or this, which is more like the stuff I read myself. Warning: SMUT, SUGGESTIVE LANGUAGE, SOME VIOLENCE. I own nothing. I'll only say it once.

-C

Decima Zimmerman was a Slytherin. She shared a room with Catarina Boatright, Glenys Groundsell, Alexis Armour, and Gwen Bittner. She was also a fifth year prefect. The other Slytherin prefects were Merita Heron and Olwen Fysshwyk, Melin Benefield and Ioan DeForest, and her boyfriend, Regulus Black.

They made their way to the front of the train to the prefects' compartment from the Slytherin compartments in the back for their meeting. She and Regulus took seats near the Ravenclaws. Decima scanned the Hufflepuffs and Gryffindors. The Hufflepuffs had the Head Girl, Ione Elam, and the Gryffindors had the Head Boy, Frank Longbottom, as well as friends of her boyfriend's brother, Remus Lupin and Lily Evans. She looked around the compartment to see who in their year had gotten the badge. In Ravenclaw, it was Miriam Bletchley and Zacchaeus Quirke; in Hufflepuff, Lucia Ellis and Pompilius Cain; and in Gryffindor, Adelle Winstringham and Osmund Ballinger.

The Head Boy and Girl stood and briefly welcomed the new prefects, assigning duties, and informing them of meetings and the password to the prefects' bathroom. When they were dismissed, Asenneth Baddock, one of the Slytherin seventh year prefects, grabbed Decima's arm and whispered the Slytherin password in her ear. It was "Cunning."

Halfway to their compartment, Decima stopped in her tracks, looking at the bag in her hands. Regulus turned and frowned at her.

"What's wrong, CiCi?"

CiCi was the nickname only her favorite people could use, which was reserved to her three best friends and Regulus.

"This isn't my bag," she said. "Someone else must have mine."

He stared at her. "But it looks just like your bag."

She shook her head and said, "No, mine's lighter than this, and it has a hole burnt into the strap from Cat's Potions debacle third year, remember?"

"Excuse me," said a polite voice behind her. "I overheard you, and I think that might be Lily Evans's bag. Yours look a lot alike, and you were sitting right across from each other."

It was Remus Lupin.

"Could you direct me to her compartment, please, Lupin?"

"I can walk you there myself," said Lupin. "I have to run her a few plans and things."

"Thanks so much," she said. "Regulus, I'll meet you back in the compartment. I won't be long."

Regulus didn't look happy, but he turned and went on his way while Decima followed Lupin into Gryffindor territory.

"I hope you don't mind," he said, "I need to stop by my compartment to grab a few things. It'll only take a second."

"Of course," said Decima, and Lupin slid back the door to a rather noisy compartment. Inside were three boys playing a game of Exploding Snap. They waved as their friend entered, who went right to work sifting through his things.

"You brought us back a girl, Remus, how sweet of you!" said one of the boys by the window, with shaggy black hair, stormy gray eyes, and a regal air about him. "How very thoughtful!"

This was none other than Sirius Black, brother of Decima's boyfriend and single-handed runner of the harem known as the Hogwarts female student body. Decima had to admit, while Regulus was very good looking, Sirius was almost too good to be a real person.

Lupin scoffed. "Don't you recognize your own brother's girlfriend? This is Decima Zimmerman. She's a prefect."

Sirius's animated face dampened considerably. He didn't allow Slytherins into his harem (okay, so it was just a fan club); it was his personal rule, or something.

"I'll be back, guys," said Lupin. "I've got to run these over to Lily. It should only take a minute."

As she followed Lupin out of the compartment, Decima couldn't get over the uneasy feeling that Sirius had just been undressing her with his eyes. What he thought gave him the right to look at her like that, she didn't know.

She followed Lupin into a compartment housing the Gryffindor sixth year girls. Lily Evans, Mary MacDonald, Desiderata Botts, Serena Fawcett and Annmarie Finnigan were talking and giggling. They looked up when Lupin knocked and entered.

"These are the plans you wanted, Lily. And this is Decima Zimmerman, one of the new prefects. We think you two might have grabbed each other's bags on the way out of the meeting without realizing it."

Evans looked down at the bag at her feet and her eyes widened with surprise.

"Oh, wow, good catch, Remus. I didn't even notice; they look so much alike! Thanks for the plans!"

They switched bags and said their thanks and goodbyes and Decima made her way back to the compartment that she shared with Regulus, his best friend, and her three best friends.

Regulus's friend, Austin Gray, was dozing by the window, and Regulus looked as though he was close to dozing as well. The three girls, Christa Rosier, Gwen Bittner, and Philomela Hayes, were fervently discussing something, and without hearing a word, Decima could be sure the topic was boys. Christa was a sixth year, and Philomela a fourth year, but the four girls were inseparable.

Decima slid onto Regulus's lap, tossing her bag on the floor and giving him a sweet peck on the lips.

"Why so glum, sweetie?" she asked.

"Listen to your crackpot friends," was his grumbled reply.

Much to her surprise, they weren't discussing just any boy, but Sirius Black, her boyfriend's brother, and the very boy who had just mentally undressed her. Apparently, Philomela had a crush on him, like nearly every other girl at Hogwarts. There was just one problem, and Christa worded it perfectly.

"Black just doesn't go for Slytherins, not even for one night stands."

"KiKi's right, sweetheart," said Gwen. "It's better just to turn your eye to someone else."

Mentally, Decima felt a twinge of sympathy for poor, infatuated Philomela. After meeting the boy once, no crush involved, Decima couldn't help but subconsciously size up her own boyfriend in comparison to the ungodly good looks of Sirius. Even his own brother couldn't compete.

"Whatever," said Philomela in her sweet, little voice. "I'll just see what happens. Forget I even mentioned it."

"That sounds like a great idea," said Regulus, wrapping his arms around Decima's waist and kissing her neck softly.

Decima had grown used to the routine of Hogwarts. She and her friends filed off the train at Hogsmeade Station, caught a carriage to the castle, sat through the Sorting and enjoyed the feast. After the feast, she and Regulus had to lead first years to the common room, which was a new part to the routine, but then they went to bed right away as usual, catching some sleep before classes stared the next day.

The next morning at breakfast, they went over their timetables and began gossiping over eggs. Regulus sat next to Decima, holding her hand, but distant.

"What's wrong?" she asked him as he poked through his eggs.

"Nothing," he said, clearly lying. "I'm just thinking about O.W.L.s."

"Oh, you'll do great!" she said, leaning over and kissing him on the cheek. "You're a talented wizard."

He continued to pick at his eggs, but brightened visibly. At least, until an atypical occurrence for the Slytherin table occurred.

Sirius Black sat down across from Decima, squeezing in between Philomela and Gwen. Regulus frowned, Philomela nearly fainted, and Decima couldn't explain it, but a blush crept onto her cheeks. How very odd.

The rouge had the audacity to wink at her before turning to his brother, who was now furious, and saying, "Hey, man, I think we may have mixed up our cloaks when we packed. Yours is a tad small for me and I've got Herbology after breakfast."

Regulus nodded. "I'll go and get it."

"No," said Decima forcefully. "I'll go and get it. You need to eat your breakfast. I don't want you passing out in Potions."

And before he could argue, Decima was leading her boyfriend's brother to the Slytherin common room. She hesitated outside it, but Sirius grinned.

"I've already been inside, remember?"

Of course. Nearly every other prank the Marauders pulled involved the Slytherins or their common room. She led him inside and up to Regulus's dormitory, where she began going through his things, looking for the cloak.

Sirius sat on his brother's bed and made small talk.

"So, how long have you two been dating?"

"About a year and a half," she replied, not looking up in her pursuit of the cloak.

"How is he?"

What sort of a question was that?

"Ask him."

Sirius barked with laughter.

"I say we do a little experiment," he murmured, standing behind her and tracing a finger along her back. She straightened up and whirled around. "We have a little test run and you tell me who's better, love."

Her eyes widened. That's what he had been asking. She could barely believe his audacity.

"What about your little rule about Slytherins?" she said, sassy as she could.

He grinned wolfishly and pulled her to him, whispering in her ear, "What about it?"-

Her heart was going nuts and her mind was racing. Why did the way he held her have to feel so good? He began to nibble on her ear and she nearly sighed. No.

No, she was not going to turn into putty for him. He was her boyfriend's brother. He was bloody Sirius Black. She wouldn't be one of those girls.

Decima turned her head reluctantly, pulling her ear out of his teeth.

"There would be nothing to compare," she said honestly. "Your brother and I haven't done anything."

Of course, that didn't put him off. He backed her into the bed and climbed on top of her, giving her a winning smile.

"Let me show you what you're missing, babe."

His lips met her jawbone, kissing and sucking at her skin. She couldn't help it. Even in biting her lip, she couldn't keep the moans from escaping her mouth. She could feel him smirk against her skin.

He bucked his hips against her and she gasped. She couldn't lose herself in this. She had to get out of there. His hands moved to unbutton her shirt and she smacked him hard across the face.

Sirius recoiled in pain and shock as she scrambled out of his reach.

"Get your cloak and get out," she said shakily. "I'm going to be late for Potions."

Decima stormed out of the room, leaving the great Sirius Black in a state of shock and rejection on his brother's bed. She wondered bitterly what his fan club would have thought of that whole scene as she straightened her clothes before stepping into class and sitting down next to Regulus.

"I told him you were doing prefect duties," he said flatly as he organized ingredients.

"You lied to Slughorn?" said Decima, hoping to sound more surprised than breathless.

"Not exactly," said Regulus bitterly. "Helping Sirius is sort of like helping first years."

She didn't say anything. She hoped the first years wouldn't jump her like Sirius had just done. But she didn't want to tell Regulus about it, knowing he'd be furious and do something stupid, without thinking.

The day went by peacefully until lunch. In fact, Decima was getting the feeling that meals were just going to become painful. Sirius wedged himself between Philomela and Gwen once more and Decima found herself suddenly fascinated by the contents of her sandwich.

"What do you want, Sirius?" said Regulus, markedly irritated.

"I realized on the train ride yesterday," said Sirius casually, "that my little brother and I had grown apart. I thought I should try to fix that. I figured we ought to be closer, ought to share things."

Decima dropped her sandwich, not daring to meet Sirius's eyes. She could feel them on her. She muttered apologies and excuses and stumbled out of the Great Hall, wondering how she was going to explain her sudden exit to her friends and Regulus.

That evening, Decima went to the prefects' bath instead of dinner, worried about talking to Regulus about her strange behavior. But there was already someone there. She couldn't see who it was through all the bubbles.

"It's me," said a voice she recognized. It was Regulus. So relieved that she forgot she had been avoiding him, she undressed and slid into the water.

But it wasn't Regulus. It was Sirius. He raised a smug eyebrow at her.

"Damn, you two sound alike," she murmured, wondering if the prefects' bath was always so hot. He chuckled.

"So that's why you got in so easily."

He moved toward her and she scooted away, changing the topic of conversation.

"How did you get in here?"

Sirius barked with laughter as he caught up with her and wrapped his arms around her loosely. She shivered.

"The password to this room is one of Hogwarts' worst kept secrets, love. Don't worry, I didn't peek."

He was now whispering in her ear, holding her against the edge of the bath. It really was hot in there.

"This is wrong," she breathed.

"But you're enjoying it," Sirius whispered, moving his hand from her waist to her thigh.

Decima hated lying. She was one of the most creative truth-benders in the school, but she never lied. In this moment, however, she couldn't think of any way to bend or deny the truth. He was right. She was enjoying it. He brushed the underside of her breast with his free hand and it was all she could do not to sigh, but his eyes met hers and he smirked. He could see the lust in her eyes.

"No," she said, pushing him off her forcefully. "We can't do this. I need to go. Regulus will be worried."

Sirius's eyes darkened at the mention of his brother's name, but he averted them as she climbed out, dried off and got dressed.

"Why are you with him, anyway?" growled Sirius.

Decima sighed as she pulled her shirt on and did up the buttons.

"Why are you playing these games? Is this some sort of competition between brothers? Is it bothering you that much that a girl would rather have Regulus?"

She could hear the smirk in his voice as he said, "You didn't answer my question, love, and judging by today, I'd be willing to bet you don't prefer him."

"I don't see how it's any of your business why I'm with him," she said in a cold voice, "and you'd lose that bet."

Sirius turned to face her and winked. Her heart skipped a beat.

"I'll take that as a challenge, love. Consider it a bet."

And then, without warning, he climbed out of the water like some kind of a sea god and shook droplets out of his hair, not bothering to cover his dripping wet, incredibly fit body with a towel as he took his time about getting dressed, amused by her shocked expression.

"See something you like?" he said with a smirk.

Did she? Oh, yes. It wasn't fair that he was so incredibly toned and muscular. He didn't even play Quidditch. Regulus did, and he didn't look quite that good. Sirius's rippling abs led her eyes downward to his shamelessly uncovered sex and she blushed, noticing his finely sculpted legs before she shook her head and turned away.

"You're absurd," she said, trying to slow her heart and clean her thoughts.

"Absurdly handsome? Absurdly charming? I've heard."

That smirk in his voice was almost unbearable. Decima watched him head for the exit. He paused just before stepping into the hall and winked at her.

"I'll see you around, love," he said suavely.

Decima took a few minutes to compose herself before heading down to dinner, thinking it was better not to delay the inevitable. She tried to seem calm and casual as she slipped into a seat next to Regulus, saying, "Hello, handsome," before pressing her lips to his.

At first, he was shocked, but then he relaxed, deepening the kiss. Decima tried to forget anyone else was around, nibbling on his lip, but Gwen flicked pudding at her.

"Oi, CiCi, up for air! We're trying to eat, here!"

Decima laughed and turned to the food, piling it onto her plate and noting her boyfriend's pathetically disappointed expression.

"Anyway," said Gwen, "what were you saying before we were so rudely interrupted, FiFi?"

Philomela sighed. "Did you see Sirius? He looks like he just got out of the shower. I wonder who he was in there with."

Decima dropped her fork and Regulus gave her a questioning look.

"What makes you say that, FiFi?" she said, trying not to look at either of the Black brothers.

"Haven't you heard that rumor that he never showers alone?"

With a genuine laugh, Decima shook her head. "I doubt that. Don't believe every rumor you hear, dear. Potatoes, GiGi."

She could feel Regulus's eyes on her as she took the potatoes, glancing across the room to where the Marauders sat. Sure enough, Sirius was still wet from their, well, whatever the hell you could call what he had just put her through. Of course, he could feel her watching him, and he met her stare, winking. She dropped her fork again and Regulus frowned.

"Are you okay, CiCi?"

"I'm just a little stressed out," she said truthfully. "I'm not really hungry. I'll see you later, sweetheart."

She made up a show of kissing him goodbye, mostly for Sirius's benefit, but Regulus didn't put up a fight. A quick glance over at the Gryffindor table, and the scowling Sirius Black was all she needed to put a smile on her face. Sirius Black, meet Decima Zimmerman. Two could play this dirty game.