I got this idea from an ask on ygofanfiction Tumblr! Also have been struggling a little bit with SetoKisa oneshots, so I figured I'd give this a go. Hope you enjoy :)

In another, parallel universe, he never had the chance to meet Gozaburo Kaiba. Over the years, Mokuba had had dreamed about this situation many times, and the reason Seto had never met Gozaburo Kaiba was always different, because Mokuba realized that Seto would have found a way to get around that, anyways. Seto could have been sick, and put on bedrest—but that wouldn't stop him from sneaking out of his bedroom to challenge Gozaburo, shaking and weak and feverish, but with bright eyes that glowed with the same determination. They could have been adopted, conveniently just days before Gozaburo arrived—but once it was announced that Gozaburo would be visiting the orphanage, Seto had become cold and aloof with prospective families, convinced that Gozaburo would be his ticket to a better life. So then, they could have been adopted before Gozaburo announced his visit—but no, Seto had tried in earnest to find a home for him and Mokuba back then, and families wanted cute newborn babies; maybe some of them wanted a solemn-faced little genius ten-year-old, but none of them wanted a bonus snot-nosed toddler who was too old to grow up believing that their foster family was truly his, and too young to not be a grubby, needy, whiny nuisance of a child. Maybe Gozaburo could have died en route to the orphanage—but that would cause too big of a ripple in the timeline, and Kaiba Corporation would still be a military company, or maybe it would have been handed to an incompetent successor and dissolved completely and caused a small-scale economic disaster. Mokuba wasn't sure of a how, but he knew, in another, parallel universe, Seto had never met Gozaburo Kaiba, and had never endured years of psychological abuse that would reverberate through every fiber of his being, and he would be happy.

The question of exactly what would have happened if Seto had never had the chance to challenge Gozaburo to a chess match, the match that Seto so proudly regarded as the moment he took control of his own destiny, was unclear to Mokuba. His brother's identity was so deeply entrenched in his passion for his work that Mokuba wasn't quite sure where he would be without it. The closest he got to a what was a familiar scene, one he had envisioned so many times throughout the years. Mokuba held dear a vision of himself and Seto at a diner in downtown Domino, at a booth next to a window where they can watch snow drift down onto an empty city street. The air is rich with chatter and coffee steam and maple syrup, and everything is soft and warm and gentle yellow inside and cold and white-blue and silent and pristine outside, and Seto holds a steaming cup of coffee in his hand. He stares out the window, watching the snow drift, and his jaw is not locked tight from anxiety from being around so many loud, happy people, or from the six meetings he has in the next seven hours, or from years of Gozaburo telling him he was pathetic, a failure, not good enough never good enough, I took you into my home because I thought you could be someone and you're nothing but the street trash nobody I thought you were from the moment I first laid eyes on you. And he turns to Mokuba, and his eyes are bright and kind and not steely-cold, and his mouth is soft and relaxed and tightens into a smile and he says, real gentle, "How are you doing, Mokie?"

He never got beyond that, beyond his alternate universe-brother's "How are you doing, Mokie?". The concept of a softer and gentler Seto couldn't be pushed too far beyond that—he lacked the capacity to imagine anything further without losing the vital essence of Seto Kaiba that made his brother who he was. When he looked at his brother, with his eyebrows furrowed as he glared at his computer screen with tense shoulders and gritted teeth, or with tightly folded arms and a haughty expression as he spat that's not my problem, were you hired to make excuses or did I hire you to do your job at a terrified KaibaCorp employee, or irritably sighing at him what is it now Mokuba, the mere existence of the concept of alternate universe warmer/kinder/more whole Seto made Mokuba feel ashamed of himself for imagining such a thing. Seto was Seto. In a million bootstrap repetitions of his life, all one million ten-year-old Seto Kaibas would have found themselves in front of Gozaburo, staring down a fully grown adult with a confident, terrified, exhilarated look in their eyes. It defied the basic principles of probability, really. If there was even the slightest probability of Seto's life being different, in some other world, some other iteration of the past, Seto would have crushed it, vanquished it, because above all, what Seto Kaiba stood for was an arrogant defiance of fate.

…

"S-sir, I completed the analysis on the strategy prediction algorithms Mr. Kaiba wanted on the virtual duelist software." A lanky man with short, close-cropped dark hair and square wire-frame glasses stood awkwardly in front of Roland's desk with a USB drive clenched in a death grip in his fist.

Roland looked up. "Mr. Kaiba requested that be delivered to his office today."

The man said nothing, adjusting his tie and wringing his hands anxiously.

"You're the head of the KaibaLand software development team. You have direct access to Seto's personal floor."

The man winced, running his hand through his hair. "Mr. Kaiba was...erratic...at this morning's software development meeting," he said slowly. Roland watched a drop of sweat roll from the man's temple and slide onto the side of his glasses.

Roland's glance flicked to the bottom of his computer screen, and then he nodded. "Ah, right. It's a special day for the brother's today, Tony. I can take the files to him personally, if you'd like."

Tony breathed a sigh of relief, setting the now slightly clammy USB drive on Roland's desk. "Thank you," he said. Now looking much more satisfied, the man nodded briskly before awkwardly shuffling away.

Roland put the drive in his pocket. Seto's chosen leader for the software development team was an unusually private, quiet man whose development talents far exceeded his leadership abilities; Roland secretly suspected that Seto picked the man because he was as stiff and brief with his exchanges as Seto, and thus the working relationship between the two was relatively unstrained. He was glad, as well, that the employee had hid his curiosity about the significance of the date so well. That today was the anniversary of Seto's game-changing chess match with Gozaburo Kaiba would be a difficult story to relay.

He had a pair of nephews about the age of the Kaiba brothers, raised by his sister in Michigan. He had just seen them over the holidays, when he went to visit them for the new year. The older boy was a sophomore computer science student at the Massachusetts Institute of Technology, and the younger boy was on an elite sixth-grade robotics team. On the first morning of his visit, the younger boy had woken up early, intrigued by the smell of the coffee Roland was making downstairs, and sat with him on the sofa, drowsily watching cartoons in blue pinstriped pajamas. Hours later, as the time drew close to noon, the older boy tumbled down the stairs. Roland remembered watching as the older boy perched himself on the armrest of the sofa, affectionately ruffling his little brother's hair. "Whatcha up to, Alex?" he had teased, grinning broadly.

"Shhhhh, Kyle! I'm watching TV," the younger boy had protested. He then had looked up at his older brother, tugging on the sleeve of his brother's red sweatshirt. "Watch with me."

"Scoot over then, kiddo," the older boy said, and lodged himself between the armrest and his younger brother, draping his arm around the younger boy's shoulder.

Roland hadn't quite been able to pinpoint at the time why the exchange between his nephews made him feel so melancholy, but he was able to connect the dots now—they were boys, young and carefree boys, smart boys, with a mother who had taken out a second mortgage to support their dreams, and who could love one another without having to rely on one another. It was exactly, he felt, what the Kaiba brothers deserved. It seemed unjust that the world wouldn't have, in time, found Seto and Mokuba a more appropriate home, where they could have been loved and nurtured, where they could have fostered their passions and their talents and honed them in more constructive ways. People liked to think that Seto was a genius because of his upbringing, but Roland knew the boy well enough to know better. Seto was always a genius, always passionate and determined; his talents never would have gone to waste even if he hadn't thrown himself headfirst into the abusive, all-consuming clutches of Gozaburo Kaiba. A picture of his nephews, taken on new years' day, smiling in front of a giant snow-tank they had constructed in their front yard, sat in a wooden frame on his desk; Roland stared at it, dreaming of an alternate reality in which he could have gone to the orphanage himself, and taken the Kaiba brothers, and raised them alongside his sister's children, and their family photo wouldn't be a thousand-dollar-an-hour professional photo of them standing haughtily in front of the fireplace they never used...

…

In the Kaiba Corporation Research and Development Journal Club, which met biweekly to discuss publications in relevant fields, it was customary for someone to bring food. Today, that someone had brought store-bought Chessmen shortbreads, square biscuits with an imprint of a chess figure on each. Though his attendance was not required, or even particularly expected, Seto had decided to drop by the journal club today. And he had forgotten to eat breakfast, and then his meeting with the head of marketing had run straight through lunch time, and although he was usually too distracted to notice these types of things, Seto was famished by the time he got to the Research and Development Journal Club. So he reached for a cookie, swallowing down half of it without looking twice. He glanced down at the uneaten half and noticed the unmistakable imprint of the top half of a chess King. Hastily, he clapped his hand to his mouth to prevent cookie crumbs from falling out.

Of course he remembered what today was. He struggled to make peace with it every year. Today, nine years ago, he had stood in front of Gozaburo Kaiba, desperately willing his shoulders to stop shaking, and challenged him to a game of chess. Tonight, nine years ago, Seto and Mokuba stood in the doorway of Gozaburo's mansion, and Mokuba clung to Seto's arm, and Gozaburo's assistant, a man named Hobbs who was short and feeble and old and still somehow entirely terrifying, showed them to their new rooms. It was no coincidence that when Seto picked his own assistant, he had gone for something of the opposite of Hobbs.

Seto didn't need Mokuba to say it to know that his brother had considerable regrets about that day. He vividly remembered Noa's reconstruction of the orphanage they lived at as children, and Mokuba shouting at him that he would change the past if he could, that he wanted his brother to smile again, that he never called him Mokie anymore. It had hurt, Mokuba's words, because until then, he simply hadn't considered a world in which they had never been adopted by Gozaburo Kaiba.

He still couldn't. Gozaburo Kaiba meant Kaiba Corp, meant Battle City, meant meeting Yugi Motou, meant everything. A world in which they had never met Gozaburo was an idiotic thought experiment; that world didn't exist. Regretting the decision that his ten-year-old self made to take control of his own destiny would mean to regret a comfortable financial future, regret knowing that his brother would always be taken care of, regret KaibaLand and the dozens of charitable organizations that KaibaCorp sponsored to benefit orphans, sick children, medical research, inner-city STEM development programs. More than that, to regret his decisions would be futile, because it was said, it was done, it was over, and no amount of wishing could change that. No amount of wishing could make him enjoy swinging on a swingset or building with blocks anymore—besides, nobody did that at nineteen years old. And no amount of wishing would make the nickname Mokie sound any less childish and idiotic than it did.

"Sir?" A woman with short grey hair who Seto recognized as Dr. Kennedy, head of virtual systems development, swam into focus. "Mr. Kaiba?"

Seto blinked, looking around. Weren't there people at every seat of the table? Wasn't the plate of cookies almost full, instead of sparsely populated with a few broken pieces? His heart hammered, and his vision doubled; he closed his eyes, attempting to ground himself with an abrupt tug to the leather cord around his neck that held his locket. He had lost time before, but it was always slightly terrifying. He was grateful that the room was empty spare him and Dr. Kennedy.

"I'm fine, Dr. Kennedy. You can go," he said briskly.

His heart sank as he heard the unmistakable grinding sound of a chair being pulled out. "Pardon my familiarity, Mr. Kaiba, but you don't look well." The woman's voice was tinged with concern; Seto hated that some of his older employees had the tendency to dote on occasion, to treat him like a child, but he couldn't hire Dr. Kennedy's experience without hiring someone significantly older than him.

Seto shook his head. "I'll be fine. You can leave," he growled.

"You'll have to excuse me if I'm not going to leave you here in the conference room alone. You look like you're minutes away from passing out."

"I'm your boss."

"And I can't in good conscience leave you here in this state. I'm gonna message Mokuba and tell him to come sit with you."

Seto grunted in response, relieved when he heard the soft clack-clacking of high heeled shoes disappear into the background.

"Seto! Seto, are you okay? I got a message from Dina Kennedy in R&D..." Seto heard Mokuba's slightly frantic voice approach. He opened one eye to find himself face-to-face with his brother, violet eyes meeting azure.

Seto groaned. "So I lost some time. I just forgot to eat," he snipped, pushing his head up and resting it on his palm.

Mokuba's lips pursed with concern. "We're supposed to call the doctor again if it keeps happening," he reminded him.

"I'm fine, Mokuba. I just forgot to eat." In one abrupt motion, Seto pushed himself out of the chair and into an upright position. The room lurched around him dangerously, and he staggered to a wall for support.

"Can we eat, at least, then?" Mokuba asked.

Seto nodded slowly, slumping down onto the floor and resting his head on his knees.

"I can call us a car," Mokuba offered.

"You want to go out?" Seto demanded irritably.

He felt Mokuba kneel down beside him, and rustle through a pocket. "Caramels," the younger boy said, gently nudging Seto's shoulder with his hand. "Your blood sugar's way, way low. You have to eat something, bro."

The buttery taste of caramel felt good in Seto's mouth; it had been a long time since had tasted something so simple and sweet. "You really need to go out to eat right now?" Seto grumbled.

Mokuba leaned back against the wall, the top of his head touching his brother's shoulder ever so slightly. "There's this diner downtown that I've always wanted to try..."

"All right, all right. I could use a cup of coffee."