Sinner's Luck

Summary: Gambling. To indulge in gambling is a sin that delves its hands into all of the 7 deadly sins. And yet, despite knowing this, he can't stop gambling. He refuses to stop gambling. In this Aquarium known as Hyakkaou Private Academy; he will gamble… All in an attempt to find someone just as twisted as him. OC-Centric. OCxKirarixHarem


I: First Gamble

"It should be coming up soon, young man," a car driver said as he drove down the busy Japanese streets. "Let me ask you to be sure though, you're attending Hyakkaou Private Academy?"

"… Yeah, I am," a soft male voice said from the back seat.

"You know, I hear lots of scary rumours about that place from students," the driver chuckled. "Lots of crazy things. You should be careful, alright young man?"

"I'll be fine, but thank you for your concern, sir."

"Ah, here it comes up now!" The driver exclaimed, drawing the young man's attention as he leaned forwards to get a better look.

Indeed, there was no mistaking it: that was Hyakkaou Private Academy. A proud school that had stood the test of time for over a century, where children from families both financially and politically powerful gathered for their education.

And yet he was but a commoner, stepping into a den far above his social class.

He let out a soft sigh and ran his fingers through his hair as the car slowly came to a stop. "Thanks for the ride," he told him, pulling out a small wad of cash and handing it over. "Keep the change."

The driver's eyes widened briefly… But hey, he wasn't going to complain about a nice chunk of money. "You need a ride back after kid?"

"No need, I've got an apartment that should be done by the time the school day finishes, thanks for the offer though," he told him, getting out of the car. He made his way to the back of the taxi, lifting open the trunk and grabbing his suitcase. "Drive safe."

"Sure thing," he nodded. "Have a fun time at school, kid! Do your best to enjoy it! You only get one high school experience after all!"

The young male only gave a soft nod as he dragged his suitcase along down the path to the school, hair white as snow swaying in the breeze. He reached to his nose and pushed his glasses up his face slightly, violet eyes almost seeming to let out a soft glow in the shadows of his face.

He didn't speak so much as a word as he made his way through the halls of the school, the only sounds heard being his own footsteps and his suitcase rolling behind him.

He finally came to a halt in front of a certain set of double doors, reading the plaque sitting proudly upon them.

Student Council Office.

He lifted his hand and knocked softly on the doors three times.

"Enter," a stern voice came from beyond the doors.

He pushed the doors open, letting them swing wide before they stopped, unveiling the room. It was simplistic, but beautiful with a long table running down the middle of the room with several chairs perfectly aligned on either side. Separated from that table was a beautiful desk made of the finest wood, an equally beautiful woman sat behind it.

Her hair was white, done in two knotted rings with ribbons, with squared bangs that had a cheek length lock on either side of her face. Her eyes were blue, the bluest eyes he had ever seen in his life, the girl wearing matching lipstick that contrasted to her pale skin.

Though he couldn't see it from his current angle, he could also tell the girl had a good figure going for her as well, with a nice bust that led down her thin sides, though that was as far as he could see.

To her right was another young woman with long violet hair done in a side ponytail, dark violet eyes matching her hair with pink lipstick upon her lips. She wore a long plaid skirt, as opposed to the short ones he'd seen in school and stared at him with her empty- near emotionless- eyes.

Behind the both of them was a giant fish tank, with various different types of exotic fish swimming around in it. It was clearly well cared for, and likely important to the girl behind the desk given she was the Student Council President.

"Mm…? Who are you?" The woman behind the desk asked, having the voice of a refined young lady, though there was a hint of boredom in her voice.

"He is the new student who transferred here on short notice," the girl beside her informed her. "Please introduce yourself."

He tilted his head as he stared at them before he bowed lightly. "A pleasure. My name is Kurogane Masamune, I transferred here from Seijoh High School. My thanks for accepting my transfer request."

"Kurogane…" She tapped her chin. "Ah yes, I remember now. Welcome to Hyakkaou Private Academy. I am Kirari Momobami, the Student Council President. To my right is Sayaka Igarashi, my secretary."

"A pleasure," Sayaka said. "My apologies for the short notice of your transfer and starting date, we were swamped with various requests and things got mixed up. As such, we'll forgive you for not wearing your uniform today. However, we expect you to wear it in the future, understood?"

"About that, is there a chance I could just stick with what I have?" He asked. "I appreciate the uniform is for formal appearances, but I don't really care for it. I'd appreciate if I could just wear what I'm wearing right now."

Sayaka's eyes narrowed. "You will wear the uniform, this is non-negotiable-."

"Then I'll gamble for it."

"… Huh?"

"Hoh…?" Kirari's eyes lit up slightly, those blue orbs almost seeming to glow.

"I said I'll gamble for it," he told them. "I've heard the rumours about this school, everything is decided by gambling, right? In that case, I'd like to gamble my freedom to wear what I like over the uniform. If I win, I get to wear what I like to school, and I get a 200 Yen coin from the president. If I lose, I'll pay the total sum of 3 million Yen, and wear the uniform without question."

Sayaka's eyes widened slightly. '3 million so casually…? On top of that, why a 200-yen coin from the president? These things aren't equal in the slightest…'

She was snapped out of her thoughts by Kirari's soft giggles. "How amusing… Very well," she put down her pen and stood up. "I'll accept that gamble."

"President!?" Sayaka exclaimed in surprise.

"Oh, don't be such a worry wort, Sayaka. This is just another disobedient student that needs to learn their place," she told her. "No need for a grand spectacle this time…" She turned her gaze to Kurogane. "Masamune-san, since I'm feeling generous you may pick the game."

"Since I'd like for us to make this quick, we'll settle this with a simple coin toss. Would you be kind enough to provide a 200-yen coin?"

Kirari raised an eyebrow in soft amusement but did fish out a coin. Why did she carry such a thing? In case of situations like these, of course, where she needed a coin toss. She couldn't rely on Sayaka for everything, after all. "Sayaka, you will toss the coin. If that's alright with you, Masamune-san?"

"I have no objections," he told her. "But I'd like you to mark the coin with your initials, to ensure no tampering can be done to it by either you or myself."

"Oh? Do you think I'd cheat?" She asked, not offended by his words in the slightest.

"No, but I like for there to be assurances. It ensures neither you nor I can cheat, nor can your secretary cheat on your behalf," he glanced at Sayaka. "Though I doubt she would. After all, to cheat would disgrace you, and a loyal secretary would never do that."

Sayaka's eyes narrowed at him dangerously. 'This arrogant man… It matters not, the president will surely win.'

"Oh, but one more stipulation," he told her. "Both of us will be blindfolded for the coin toss."

Both Sayaka and Kirari looked at him, both of them having surprise on their faces.

"Furthermore," he continued. "Neither of us will know the result of the Coin Toss. Igarashi-san will tell us the result, and she can either tell the truth or tell a lie, and that will be accepted as the result."

"How interesting…" Kirari smiled. "How very interesting. I agree," she pulled out a marker and wrote her initials down on the coin on the heads side, before setting it on the table. "Sayaka, blindfold me."

"Y- yes," Sayaka nodded, quickly retrieving a cloth and wrapping it around Kirari's eyes, preventing the President from being able to see a thing.

As for Kurogane, he removed his tie and glasses, placing his glasses on the table and wrapping the tie around his eyes, making sure it was done properly so he couldn't see anything. Sayaka made her way over and made several motions that would have made him flinch if he could see her actions, but he didn't so much as twitch.

Satisfied that they were both thoroughly blindfolded, she lifted up the coin, ready to flip it.

"Please announce when you have flipped it, Igarashi-san," Kurogane spoke up. "While it is in the air, Momobami-san will call it, heads or tails."

"Hm hm hm… Very well, I agree," Kirari said. "Flip when you are ready, Sayaka."

Sayaka hesitated, double checking the coin to be sure it wasn't gimmicked or tricked in any way, shape, or form. Kirari may have provided it, but she would make sure it wasn't rigged.

Satisfied it wasn't, she placed it on her thumb. "Ready? And… Flip!" She flipped the coin into the air.

"Tails," Kirari spoke up as the coin hurtled through the air before Sayaka caught it, covering up the result.

"… Before I reveal the result, I would like to ask you something, Masamune-san." Sayaka spoke up.

"Go ahead, Igarashi-san."

"Why would you accept me flipping the coin? No, more importantly, why would you accept the result even if I lied? Could I not guarantee the president's victory this way?"

"You could, easily, and I would be forced to accept that," he told her. "But this is what it means to perform an all-or-nothing gamble, Igarashi-san. My gamble on whether Momobami-san called the toss wrong, and my gamble on if you'll be willing to admit she lost if she did."

"Ara… What an interesting young man that's stumbled into my Aquarium," Kirari grinned slowly, the same kind of grin she always showed whenever she was excited. "Very well, what say we up the stakes of this game then, Masamune-san?"

"You have my attention."

"If I win this game, you will be my personal pet," she told him, making Sayaka suck in her breath in shock.

Despite creating the discrimination system in the school, the President had never used it to have someone be her personal pet. And yet she'd been around this man for a few minutes, and yet she was willing to take him in?

"And what do I get if I win?"

"What do you want?"

"Hm, that's a good question. If I win… Hm, my apologies, I can't think of anything off the top of my head. How about the Student Council pays off the first debt I receive should I enter debt at this Academy?"

"Oh? I see someone's been doing their research on my school… Very well, I find these terms acceptable."

"With the gamble having been updated, I will now reveal the result of the gamble," Sayaka declared. "The winner of the match is…"

"…"

"…"

"… K… Kurogane... Masamune… Is the victor…"

Kurogane smiled as he removed his tie from around his eyes, those violet orbs of him glowing brightly as Kirari slowly reached up and lowered her own blindfold, her blue eyes showing genuine shock within them.

"Looks like I win," he told them, both girls standing in still shock. He stepped over and plucked the coin off of the back of Sayaka's hand. "As reward for my victory, I'll be taking this 200-yen coin. Oh, and I'll be wearing what I like to school instead of the uniform from now on. But don't worry, I won't wear anything immodest at all. I'm fine with what I have on now," he gestured to his worn jeans, black button up shirt with the sleeves rolled up, and the white tie he did up to hang loosely around his neck.

"How…?" Sayaka whispered. "How did… That shouldn't be…"

"And yet it is," he told her. "There was nothing special I did, Sayaka-san," he plucked his glasses off the table and put them on. "Just pure luck, and nothing more."

"Luck…?" Kirari spoke up. "Luck? Here I thought you had some sort of strategy, and yet… You did nothing? Then why the charade of blindfolds and even allowing me to choose a coin, and letting Sayaka to flip it?"

"To limit us," he told her. "Some people are able to follow a coin as it flips, able to tell when it lands on heads or tails just by looking. With us wearing blindfolds, that benefit is removed. Some people can also determine it by sound alone, however, and I had no way of knowing if you'd trained your ears to do such a thing. In the end, it all came down to a gamble on if you'd call the right or wrong option."

"But what about me?" Sayaka asked. "There was no guarantee I would call the result in your favour, even though it was your victory. I could have easily called things in favour of the president."

"Didn't you hear me?" He tilted his head, violet eyes glowing brightly as the room seemed to grow dim. "I gambled. I don't know enough about you or the prez here to determine your personalities or the choices you'd make. So, I took a risk. I took a risk on if you were an honest person who would keep things fair, or if you were a biased person who would rig things in favour of the president. Thank you for allowing my gamble to pay off, Igarashi-san," he flipped the coin into the air before catching it. "I greatly appreciate it."

Sayaka stared at him, her body trembling lightly. 'He… Gambled…? He risked incurring a 3-million-yen debt on pure luck? I… I don't understand. Where's the logic in that? No strategy beyond limiting the president, only praying for the best…? I… I don't understand. I can't understand.'

"My…" Sayaka's gaze was drawn to Kirari, only for a shudder to course through her spine as she saw the wide, almost face-splitting smile she had, her blue eyes glowing brightly. "How very fascinating… How interesting you are, Masamune-san… How would you like to join the Student Council?"

"President!?" Sayaka exclaimed in shock.

"No thank you," Kurogane responded, making Sayaka whirl around to him in shock. "I didn't come to this school to join the student council; I came here to have fun on my own terms."

"Oh?" Kirari raised a delicate eyebrow.

"You see, I like to play my own way, so I'm going to turn this school upside down…" He lifted up the 200-yen between his fingers. "Thanks for the 200-yen, Momobami-san. It will make a nice souvenir," he slipped it into his breast pocket. "Now then, could I have my schedule please? That's the original reason I came to this room, after all."

"… Very well, Sayaka."

"Eh? Ah… Yes," she nodded, pulling out a sheet of paper and handing it over to him. "This is your class schedule, Masamune-san. You will be in the Second-Year Hana Class…" She hesitated briefly before she wrote out a note and Kirari slowly stamped it, handing it over too. "And this is your note to give to your teacher that will allow you to get away with not wearing the uniform."

He nodded as he took the schedule and note and looked them over. "My thanks, Igarashi-san," he bowed and made to leave before pausing. "Oh, and I have a small request you're free to ignore. Please don't tell anyone about this gamble of ours."

"Huh?" Sayaka blinked… Why did he not want anyone to know about him defeating the president?

"After all, I don't want people to get intimidated by me when they learn I beat you, that would make finding other people to gamble against such a chore."

He didn't wait for so much as another word from them, making his way out of the room, suitcase trailing behind him.

"Ah…" Kirari Momobami's smile only widened as she watched the young man who had defeated her leave the room. "It seems an exotic fish I never expected has entered my Aquarium… I can't wait to see how things end up as a result…"


Kurogane let out a yawn as he walked through the halls, looking down at his class Schedule. Thanks to his little impromptu gamble with Kirari, he was running a bit late, but he didn't really care too much about that.

"Let's see," he looked at his Schedule. "Second-Year Hana Class, is it…?" He mumbled to himself as he confirmed his class, the only sounds in the halls being his footsteps and the rolling of his suitcase.

He finally arrived at his destination and knocked on the door.

"Come in!"

He pushed open the door and made his way in, pulling in his suitcase with him. "My apologies for being late," I told the teacher. "There was a mix-up with my starting date, so I barely arrived on time. And due to the mix-up, it took a little while for me to receive my schedule."

"That's fine, it happens," the teacher nodded. "Why are you not wearing your uniform?"

I handed over the note from the Student Council and she read it before her eyes widened slightly. She quickly schooled her expression and then nodded, turning to the class.

"Class, as you are aware, we were due two new students today. First was Yumeko Jabami. This is the second, please introduce yourself."

He nodded and grabbed a piece of chalk, writing his name on the board before turning back to the class. "My name is Kurogane Masamune. Just call me Kuro, it's less of a mouthful. I suppose I should say a bit about myself, since it is the middle of class and we don't have time for questions, so I'll just cover the basics people normally ask. I am single, I'm not looking for a girlfriend, I moved here because my old school wasn't meeting to the standards of education I wanted, my hobbies are reading books, including shitty fanfictions online, and occasionally blacksmithing."

Everyone looked slightly confused by the mention of my last hobby, but the teacher just nodded. "Suzui-san," she spoke up, drawing the attention of a brown-haired girl in the front row. "I'm aware you will be showing Jabami-san around, but I will be leaving Masamune-san in your hands as well."

"Eh? Ah, yes," she nodded.

"Good. Masamune-san, please take a seat next to Jabami-san. Jabami-san, please raise your hand."

He saw a hand lift, his eyes landing on a gorgeous young girl with a curvaceous figure, long red hair, and burgundy eyes… He would almost call her a typical Yamato Nadeshiko based on appearance alone. He made my way over, giving her a quick nod as he took a seat at his desk, slipping the suitcase under the table for now.

Class slipped by rather quickly, and soon enough Ryuko Suzui was showing around both Yumeko and Kurogane.

"Wow," Yumeko marvelled as they walked past the gardens. "It's so beautiful here, such a marvellous academy. I'm so glad I transferred here."

Kurogane hummed softly as he looked over the scenery. Yes, it was pretty… But it wasn't what he'd come to the academy for. Not by a long shot.

"Let me introduce myself to both of you properly now, if you don't mind," she smiled. "I'm Yumeko Jabami. It's lovely to make your acquaintance."

"You too," Ryuko responded. "I'm Ryuko Suzui. As you know, I'm the class rep. It's nice to meet you both too."

"And you both know me," Kurogane responded. "But since we're being all polite, I'm Kurogane Masamune, nice to meet you both too. Just call me Kuro."

"Of course, Kuro-san!" Yumeko smiled. "Then please, both of you call me Yumeko!"

"W- Wow, both of you are quite informal," Ryuko noted. "Um, I'm a bit uncomfortable using my first name so casually, so just call me Suzui for now, if that's okay? Once I get used to both of you, then you can use my first name."

"Of course, completely understandable!" Yumeko smiled, before she noticed the tag resting against Ryuko's chest. "Suzui-san, what is that tag? It says… 'Kitty?'"

Ryuko instantly tensed up and turned away, making Yumeko tilt her head curiously, while Kuro shifted his gaze to Yumeko.

Given the fact the girl didn't know, it seemed she hadn't done her research before she came here. That, or she was deliberately acting ignorant about what she did know. He was banking on the former, but it honestly didn't matter that much. She would learn.

"Yumeko, Kuro-san… How good are you at gambling?"

"Gambling?" Yumeko questioned. "I know the general rules for poker and mahjong and the like."

"I don't know anything about mahjong, so you have me beat there, Yumeko," Kuro told her. "I'm a decent shake at gambling though, why do you ask Suzui?"

"I guess you must not know…" She told them, back still turned. "You see, gambling has been traditionally prevalent in our school. Once the bell rings, gambling stations pop out across campus. And there are plenty of rich students, so the bets are nothing to scoff at. They'll… Probably ask you both to play soon, so please be careful-!"

Yumeko began to giggle, drawing Suzui's attention as the girl turned to look at her.

"Well, well," Yumeko practically purred out. "I'm definitely looking forward to receiving such an invitation."

This instantly drew Kuro's interest as he looked at her intensely. "You're excited to gamble, are you?"

She looked at him and smiled. "Yes, it sounds quite fun, don't you think?"

"Hm… I suppose it does," he agreed as he returned her smile with one of his own.

"A- Are you both crazy…?" Suzui asked. "Well… I can't say I didn't warn you both, at least…"


As soon as the bell rang, Kuro got up and left the class with his suitcase. He had no interest in socialising with the class at that moment, there was gambling to be done. And he wanted to look for someone to play against.

Soon enough, he arrived at one of the Gambling Halls. Many tables had been set up with various games just like in a casino. His eyes glazed over all the games, before he spotted an interesting table that seemed to be playing five-card draw poker.

Why was it interesting?

Because sitting at the table was the Student Council President herself, Kirari Momobami, with Runa Yomozuki overseeing the game.

He felt his fingers start to twitch, his breathing picking up slightly as a grin slowly worked its way onto his face… Even though he'd gambled with her earlier, he just couldn't help himself. After all, he knew very well who Kirari Momobami was.

A girl chosen by the God of Dice.

That was why he had to face her a more serious gamble. He'd go crazy if he passed up this opportunity.

He walked forwards slowly as someone at the table broke into tears and collapsed onto the ground, curling up and sobbing as they lost the rest of their chips.

"And another one bites the dust!" Runa laughed. "How amusing! Everyone knows playing against the president is suicide, after all!"

"What's the buy in?" Kuro asked once he reached the table.

Runa's laughter stopped and she looked at him. "Hm?"

"What's the buy in?" He repeated.

"Buy in? You wanna face the president along with the rest of these schmucks?" She smirked. "Go ahead, 10 million yen for 1 chip."

"I'll buy 10 chips," he told her, pulling out a huge stack of cash from his suitcase and tossing it at the short girl, who caught it as he took a seat at the table.

Runa hummed as she flicked through the cash to check it before she nodded and pushed 10 chips in front of him, dealing him in for the next hand.

"I wasn't expecting we would meet again so soon, Masamune-san," Kirari spoke up as she lifted her cards, looking over them.

"Nor did I," he told her. "But if you're gambling, then there's no way I could pass up such a chance. Such a high-stakes gamble… There's no way I could ever ignore such an opportunity."

"Tch, you're just a newbie," someone at the table said scornfully. "You have no idea what you just signed up for. Ten chips won't last you long."

Kurogane only smirked as he lifted his cards, looking over them, before he pushed his chips forwards. "I'm going all in."

The entire table looked at him in surprise.

"Tch, idiot," the guy scoffed. "I call!"

"Call," the girl beside him agreed.

"I fold," Kirari told them, dropping her hands down on the table face down.

"How many cards are you trading in then?" Runa asked.

"Two," the girl said, turning in the 4 of diamond and the three of spades.

"One," the guy said as he gave up the Queen of Hearts.

"Four," Kurogane responded as he gave up… All four aces.

Both the guy and girl at the table looked at him like he was crazy, Runa just raised an eye, while Kirari had an amused look in her eyes.

"Are you crazy!? You just tossed away four ages! That's the best hand in poker outside of a fucking Straight Flush and a Royal Straight Flush!"

"I'm happy with my choice," he told them.

Runa dealt out the cards, and Kurogane looked at his hand, nodding lightly when he saw it.

"Now then, everyone happy? Then showdown!"

"Three of a kind, queens!" The girl said as she showed off her hand.

"Full House, Jacks full of 10s!" The guy said with a smug smirk, sure that there was no way Kurogane would get lucky after tossing out four aces.

"Four of a kind," Kuro revealed his hand. "Kings."

The girl and boy both froze, staring in shock at the hand he played. "… W- What?" The boy choked. "That's… That's impossible, you're cheating!"

"I am?" He chuckled. "Where's your proof? Unless you are implying that, somehow, I've convinced the Dealer to aid me in cheating?"

"You'd better not be implying that," Runa said, her smile gone as she looked at the boy with a cold, dangerous gaze.

The boy gulped and backed down but glared at me. "Don't think you'll wind the next hand! You can only be lucky for so long!"

Kurogane only smiled.

"All in."

"All in."

"All in."

"All in."

Over and over, it repeated as the new student boldly and without fear went all in on every single hand he received, never failing to lose. Somehow, almost impossibly, his hand would just be better. The strongest hand was a two pair, he'd be holding three of a kind. Four of a kind, he had a straight flush.

20 minutes. In only twenty minutes, both the boy and girl at the table had left, sobbing to themselves after being utterly crushed, leaving only Kirari and Kurogane at the table.

In the entire time he'd been playing, Kirari had never once played a hand, instead watching in pure amusement as he decimated the poor souls that had challenged her without a care in the world.

"My, my, who knew you were such a savage person," Kirari said to him, her ice blue eyes glowing brightly.

"Those who cannot gamble, cannot live," he told Kirari, removing his glasses as his violet eyes glowed with an equal intensity to hers, the two having a small staring contest.

Kirari had over 500 chips sitting in front of her, while Kurogane wasn't far behind with 300 or so chips.

Kirari smiled slowly. "Ahh… I haven't been this fascinated with someone in so long… Shall we play then, Kurogane-san?"

"No thanks," he stood up, making both girls blink in surprise. "I've fleeced enough winnings out of these weaklings for today… And besides, Momobami-san… We shouldn't be playing for this mere pocket change."

She giggled softly. "You call a total of 8 billion between us pocket change?"

"Yes," he nodded. "Make no mistake, Momobami-san. We will play a game someday. And when we do, it won't be for this chump change few billion yen… When that day comes, I will put my very life on the line to give you the most thrilling and exciting gamble of your very existence."

Kirari visibly shuddered with a grin on her face. "You really shouldn't sweet talk me like this, Kurogane-san. People might get the wrong idea."

"Call me Kuro," he told her. "And I'm not sweet talking you, just stating facts… When we play, it will be all or nothing, life versus life. When the day comes that we have our game, we'll bet all of our being, our very souls in order to determine the victor."

"Oh?" Her eyes lit up in amusement. "You'll make me a house pet?"

Gasps echoed all around from the sheer audacity of those words.

"Who knows?" He told her. "If that day does come, I'll make sure to treat you nicely, Momobami-san."

"Oh please, call me Kirari," she smirked, blue eyes glowing brightly. "You've talked a big game, Kuro. Please, don't disappoint me by the time comes."

"Oh, trust me, Kirari…" His violet eyes glowed brightly. "It will be a gamble you'll never forget for the rest of your life."

What they all witnessed that day was a promise for a match that would be spoken throughout the school, both long before and long after it occurred. A match between two like-minded individual who just wanted to enjoy the thrill of gambling, even willing to bet their very lives for the sake of pure enjoyment.

They beheld a promise that would change the world.