Hello, to my new readers! And to my old ones, hi there again! Yup, look at me starting a new story. Despite the fact that I currently have three ongoing stories. And despite the fact that I've repeatedly told myself that I should NOT be starting a new story when I have three ongoing ones, two of which desperately need to be updated soon. However, this idea would not leave me alone and so I have to put it down. And so, here we go, I've started a new story. I am by no means abandoning the other stories, I am just doing something new. Writing something new keeps me from getting bored with everything else.

I watched Big Hero 6 on the day it premiered and I LOVED IT! Like seriously, I was so pleasantly surprised by how good of a movie it was. I had been getting hyped for months about this movie, ever since I saw a teaser trailer many months ago. But I was so worried that the movie would not live up to the hype. But then I saw it and I loved it so much. Hiro Hamada has been added to my list of fictional sons and Tadashi Hamada has been added to my list of fictional crushes. Everyone in the cast is just so lovable…except masked bastard, screw him with a rusty spoon.

Before we go into the story, let me explain what I have in mind. The AU this story will present is one of my guilty pleasure AUs. I really love this AU a lot, even though it is a painful one. I'm not specifically mentioning what AU it is because I want to kind of make it a surprise. I'm sure a good number of you know what this AU will be about but for the rest, just wait and you'll see. I hope to keep the story true to the original while new enough as well. Also, this is honestly the first time I'm writing a multi-chapter fanfic without having a physical copy of the source material. Well, the movie's still super fresh in my mind and I can always do my internet sleuthing if I can't remember something properly. The first couple chapters are going to just be introductory stuff. Once we get into the movie timeline, then comes the thing that drives this into AU territory. So, without any further distractions, let's get into the story! I hope you all enjoy it!

Disclaimer: Disney and Marvel are the ones who own Big Hero 6. I have no part in this glorious movie.

"Tadashi, honey, don't be like that…"

Six year old Tadashi Hamada's pout grew bigger at his mother's words. He drew himself up into a tighter ball as he lay on the couch, fiddling away with the toy robot his father had gotten him for his birthday the week before.

He heard his parents sighing. He wasn't taking the news as they had expected, but he didn't care. You see, Tomeo and Marie Hamada had come back from the doctor's office with what they thought was exciting news.

Tadashi Hamada was going to be a big brother…and he didn't like that at all.

Tadashi had heard about what it was like to be an older sibling from the other kids at school. He'd seen what it was like too. Parents never had time for the oldest anymore, focusing all their attention on the new baby. They spoiled the baby rotten while the older one got left behind. A boy in his class had told him about how his little sister always got away with messing up his stuff since she's his parents' "precious angel". One of the girls talked about how her little brother's crying has kept her up all night. Tadashi had seen a couple younger siblings do something wrong, only to get the older sibling in trouble. Because it was the older sibling's "job" to look out for the younger ones.

If that was how being a big brother was like, then Tadashi wanted no part of it. He wanted his parents' love all to himself, thank you very much.

"Tadashi," his mother said softly, taking a seat beside where he was curled up on the couch, "C'mon, sweetie, I know you'll be a wonderful big brother."

"I don't want a baby," the six year old mumbled, a frown planted firmly on his face as he twisted his robot's arm this way and that, "Cancel the order."

"Tadashi, that…isn't exactly how it works," his father replied, amusement in his voice, "You'll love your new brother or sister, I'm sure you will."

"No, I won't," Tadashi answered, sitting up and glaring at his father, "Being a big brother won't be any fun. The other kids said so."

"Well, they're new to being older siblings," Mr. Hamada pointed out, "I probably would've acted the same way if I ever had a sibling."

"I was that way," Mrs. Hamada added, "You know how your Aunt Cass is my little sister, right, Tadashi? Oh, I remember crying and begging my parents to take her back when I first saw her at the hospital."

"Marie…" Mr. Hamada began warningly, looking at the way Tadashi stared at his mother.

"She never seemed to stop crying either!" Mrs. Hamada continued on, too lost in memories, "I was practically falling asleep in class for the whole first year!"

"Marie…"

"And that little weasel was always drooling over all my stuff. I got so mad when I saw her chewing on my favorite book."

"Marie…"

"And do not get me started on that time with the go-kart and that ice cream truck! My parents never let me hear the end of that one-"

"Marie!"

Mrs. Hamada jumped at her husband's shout before following his finger, pointed at their son. She chuckled sheepishly at the horrified expression on Tadashi's face.

"Yup," Tadashi decided as he jumped off the couch, "I don't want a baby!"

With that he ran out of the living room, headed towards his own bedroom. That decided it. There was no way Tadashi would ever like this new baby. He only hoped his parents would understand and decide to cancel their order after all.

Nine months passed and Tadashi found himself waiting with Aunt Cass outside the hospital room his parents were in. His parents, despite Tadashi's arguments, had decided not to cancel their order for the baby.

Tadashi had to admit that while he still wasn't very excited about the baby, he'd become more interested in the idea as the months had passed. He had been curious as he saw his mother's stomach getting bigger and bigger. He wasn't sure why his parents laughed when he asked how the doctor fit the baby in there.

Sometimes he'd go to ask his mother something, only to spot her gently rubbing her stomach with a really sweet smile on her face. He had asked his father this and that about the baby, even helping to set up the nursery.

Tadashi remembered his parents telling him how the baby was going to be a boy. He had to admit, a part of him was interested about that. A little brother…

Tadashi still didn't want the baby to steal his parents' love from him though.

"Oh, aren't you excited, Tadashi?" Aunt Cass asked, "You're gonna get to meet your new baby brother!"

"Yeah…" Tadashi mumbled, swinging his legs as he sat restlessly in the chair.

Aunt Cass raised an eyebrow at his behavior, leaning a little closer to the six year old.

"What's the matter?" she asked him, gently turning his face to look at her, "Your brother isn't even here yet and you're already tired of him?"

Tadashi only furrowed his brow a bit at her questions, looking away before pulling his knees close to his chest.

"Well, I gotta say you're lucky you're the older one," Aunt Cass told him, "Being the younger sibling is tough, trust me on that!"

"R-really?" Tadashi was surprised at that, "What's so bad about it?"

"Oh, it's not that it's bad, really. It's just kinda tough. I mean, growing up I always thought I could never be as great as Marie. She's beautiful, funny, cool-"

"But you are cool, Aunt Cass!" Tadashi exclaimed.

"And you're a man after my own heart, aren't you?" Aunt Cass smiled, putting a hand over her heart, "Well, I guess I'm cool. But back then I didn't think so. I always thought Marie was better at everything. And she was always way smarter too. No one was surprised when she became a lead researcher at the San Fransokyo Robotics Lab. I remembered feeling so proud, yet jealous too because she just seemed to be doing more and more amazing things in her life."

Aunt Cass grinned at Tadashi before ruffling his hair.

"But if she didn't do those things she'd have never worked with your dad and then we wouldn't have you or your brother."

"You don't hate Mom, do you, Aunt Cass?" Tadashi wondered.

"No way!" Aunt Cass laughed, "I love Marie to bits! Sure, we've argued a bunch over the years. We've said mean things to each other. And we've gotten each other in trouble before. We've always competed for our parents' attention."

Aunt Cass closed her eyes and smiled softly, as though lost in her memories.

"But we still love each other. We cried and laughed together. We've shared secrets and protected each other. We've encouraged each other too. I helped Marie realize how much she wanted to pursue a career in science. She helped me to stop trying to please our parents and do everything she had done. She saw how unhappy I was and helped me realize how much I wanted to run my own café."

"So…" Tadashi started after a moment, "Is it hard or easy? Having a sibling?"

"…Both," Aunt Cass answered, "Sometimes one, sometimes the other. But at the end of the day, it's both."

That wasn't exactly the answer the six year old had been hoping to get. Tadashi wasn't sure he quite understood what Aunt Cass meant.

"Hey, guys."

Tadashi and Aunt Cass turned in the direction of the voice to see Mr. Hamada standing at the door to the hospital room, a tired but happy expression on his face. Mr. Hamada squatted down to be at eye level with Tadashi.

"You wanna meet your little brother, Tadashi?" he asked.

"…Okay…"

The room was big and the walls were white, except for the blue banners and bright balloons brought by Aunt Cass and other well-wishers. In the big bed was Mrs. Hamada, sweating and looking absolutely exhausted, but still managing to smile brightly.

"Hi, sweetheart," she whispered when Tadashi approached the bed, "You're a big brother now."

She tiredly pointed at a smaller bed on wheels that was next to hers. Tadashi could hear some soft noises coming from the small bed, but it was too high up for him to see inside. Mr. Hamada picked up the six year old to give him a proper peek at the bed's contents.

"Tadashi…Say hello to Hiro."

The baby, Hiro, was…tinier than Tadashi had expected. A tiny thing with pinkish skin and eyes firmly shut. He was wrapped up snugly in a dark blue blanket, a matching cap atop his head, a couple small tufts of black hair peeking out beneath the little hat.

"…He isn't doing anything," Tadashi noted.

"He's sleeping," his mother replied, "Babies will sleep a lot."

Tadashi tilted his head, continuing to stare at the little guy who would now be his baby brother.

"So what's the verdict, little man?" Aunt Cass questioned, a grin on her face.

"…I guess he's kinda cute…"

Mr. and Mrs. Hamada had been quite pleased about the development between Tadashi and baby Hiro. Tadashi had shied away from the infant for the first week or so. However, the six year old's curiosity soon got the better of him. Tadashi would ask to be lifted up to peek into Hiro's crib. When his parents would hold the baby, Tadashi would poke Hiro's cheeks gently, watching him closely.

Sometimes, Mr. and Mrs. Hamada would peek into Hiro's nursery, only to spot Tadashi there, standing on the nearby bed to get a good view of the crib next to it. He'd be showing off one of his robots or an invention he came up with, talking excitedly about it and carefully holding it out to give Hiro a peek at it. Hiro, usually a rather quiet child, would babble quite a bit in return.

As the months passed, sometimes the proud parents would try and let Tadashi hold his baby brother. Of course, the first few episodes weren't quite so nice, with Tadashi putting his face a bit too close, causing Hiro to excitedly grasp his nose or yank on his hair. While Mr. and Mrs. Hamada worried that this would deter their older son from interacting with the younger one, they were surprised by how many times Tadashi wanted to try again.

"I'm not giving up on you," the six year old would say determinedly to Hiro before plopping on the couch and asking to hold the baby again.

Eventually, Tadashi got the hang of holding Hiro without resulting in another painful yank. Mr. and Mrs. Hamada smiled as Tadashi would giggle over the silly noises Hiro made as he reached for his big brother's face.

There were little fights, of course. Tadashi was never too happy to see Hiro putting his mouth on and slobbering over a project he was working on. And there were times when the crying was too much for Tadashi to take.

But Tadashi seemed to take to the idea of big brother better than Tadashi himself had expected. And little Hiro seemed to be quite devoted to his big brother.

After all, Mr. and Mrs. Hamada saw how, when Hiro was old enough to start crawling, the baby would chase after Tadashi whenever he could, despite the fact that he was usually too slow to keep up with the older boy. Tadashi, in return, would often grin when he looked over his shoulder and spotted a familiar little figure trailing after him, purposefully slowing down.

"C'mon, Hiro, come to Daddy!"

"No, come to Mama, Hiro!"

"Are we really competing over this?"

"We compete over everything, Tomeo."

"True…"

Tadashi looked up from his homework to laugh softly to himself over his parents. Mr. and Mrs. Hamada were each a foot away on opposite sides of one year old Hiro, who was standing on unsteady little legs, holding a nearby table to support himself. Hiro had taken a few steps before, only to fall down quite quickly. But, in true Hamada spirit, the kid kept trying again and again. And now, Mr. and Mrs. Hamada were competing to see who Hiro would walk to first.

The now seven year old Tadashi had returned his focus to his homework for just a few minutes when he heard his mother shout.

"Tadashi, look!"

Tadashi turned his head and his eyes widened. Hiro…Hiro was walking! Walking in his direction!

The seven year old jumped out of his chair and knelt down, holding his arms out.

"C'mon, buddy, you're almost here!" he said encouragingly while his mother was ordering his father to grab the camera quickly.

Hiro was just a few steps from Tadashi, arms reaching out for him as usual, when he stumbled and started to fall. Tadashi acted quickly and caught the baby before he fell on his face.

"Nice one, Hiro!" Tadashi exclaimed, smiling broadly at the child in his arms.

Hiro giggled in return, reaching for Tadashi's face. As Tadashi played with his little brother, he heard his father moan pitifully in the background.

"I can't believe we lost to the big brother again…"

"C'mon, Hiro, say 'Tadashi'."

"Dashi!"

"No, bud, it's Tadashi…"

"Dashi, Dashi!"

"You're forgetting the first part of my name."

"Dashi!"

"…Well, I guess I can be Dashi for now."

"Okay, ready, Hiro?"

The now two year old Hiro stared at eight year old Tadashi with a determined grin. Tadashi had been trying to teach Hiro a special handshake for the two of them to have. Sure, it may have been a bit too much for a two year old to remember, but that didn't stop either of the boys from trying.

"Okay, first it's like this," Tadashi said slowly, manipulating his brother's hand for the first part of the handshake, "Now, make a fist. And we fist bump. Ready for the last part?"

Tadashi then pulled his hand away from Hiro's, releasing the fist and making an explosion noise. Hiro immediately laughed at hearing the noise.

"Again, again!" Hiro cried, sticking his hand out to do it again.

"Alright, let's do this."

"Hiro!"

The two year old seemed to look a little ashamed at being caught playing with the robotics kit Tadashi had gotten for Christmas by none other than Tadashi himself. Tadashi had his hands on his hips and a frown on his face. He was about to scold Hiro until he saw what his little brother had done.

"W-wow, Hiro," Tadashi's voice was full of awe as he got closer, kneeling down beside his brother, "You already put half of it together!"

"Cool, right?" Hiro asked, smiling as he held up the half completed robot.

"Real cool," Tadashi nodded, ruffling Hiro's hair, "Man, you did a nice job with it."

"Need help."

Hiro held out a strange piece. Tadashi recognized it as a piece he himself had trouble with. The piece didn't seem to fit anywhere on the robot, yet Tadashi knew it was indeed part of the kit and so it had to go somewhere.

"Well, you know what Mom and Dad say," Tadashi tried to deepen his voice to imitate his father, "'Every problem has a solution. If you can't figure it out, just look at it from another angle!'"

"Huh?"

"Well, if you can't figure out the answer, just look at the problem differently, and maybe that'll help!"

Hiro nodded at the explanation before trying, and failing, to do a handstand.

"What're you up to, knucklehead?" Tadashi asked, trying not to laugh at his brother's repeated attempts to do a handstand.

"I'm looking differently!" Hiro replied, groaning after another failed attempt.

"I…don't think Mom and Dad meant it literally…But why not?"

Tadashi joined Hiro's attempts at doing a handstand, both trying to solve the mystery of the strange robot piece. Neither of them were aware of their parents lurking at the doorway with cameras in their hands.

Tadashi Hamada was not jealous…Okay, maybe a little…

It had to do with his three year old brother. A couple weeks earlier, his mother had left a paper covered in complex calculations behind on the table. When she had returned for it, she had found Hiro using his crayon on the paper. Mrs. Hamada had taken it away, worried that the notes were ruined.

However, she was utterly stunned to see that Hiro had actually written out solutions to half the problems in crayon…And the solutions were correct.

After that, Mr. and Mrs. Hamada went out with Hiro to some doctors. The news they got was amazing. Hiro Hamada was a child prodigy, his IQ far above the average for his age. He was able to solve scientific and math problems that were advanced, even by researching standards.

Three year old Hiro Hamada was a certified genius.

Tadashi had been stunned when he overheard his parents talking about it excitedly, gushing with pride over their little boy. Hiro was over in the corner, apparently focusing on his coloring book. But, from the pink color on his cheeks, it seemed the toddler was well aware of the praise he was getting.

Tadashi had taken a peek at the calculations that Hiro had solved. His head was hurting in seconds and he couldn't figure them out, not even Hiro's little solutions.

Now Tadashi was smart too. It seemed to come with being the son of two top robotics researchers. He was pretty advanced for his age, working out problems and reading books several grades ahead of where he was.

But nine year old Tadashi was not the same kind of smart three year old Hiro was.

Tadashi was really proud of his baby brother, for sure. But he couldn't help but feel envious too.

"But…You promised!"

Tadashi was angry as he looked back and forth from his mother to his father. Hiro, who was in his mother's arms, seemed unaware of the tension as he played with the robot Tadashi had given him earlier.

Four months…He had been eagerly waiting for four months! They had promised him four months ago that they'd take him!

There was a giant week long robots expo going down in the heart of San Fransokyo. Scientists and students from all over the world would be showing off the latest bits of technology. Tadashi had begged and pleaded and finally his parents had managed to get a day off from work so they could attend the expo.

But now, there was a change of plans.

"I'm sorry, Tadashi," his father said, putting a hand on the nine year old's shoulder, "I know how much you wanted to attend the expo. But the doctors really needed us to bring Hiro in to check on his development."

"But can't you reschedule?" Tadashi asked, "You promised me first!"

"I know, dear, we tried but the doctors couldn't make it any other day," his mother explained.

"But…Robert Callaghan is gonna be there!"

Robert Callaghan was one of the leading experts in the field of robotics, considered by many to be one of the pioneers in the advancements of recent years. He was one of Tadashi's idols and this expo was supposed to be his chance to finally meet the man he admired so much.

"We're really sorry, Tadashi," his mother said, "The next time the expo comes we'll make sure to take you. But today we really need to go with Hiro. You can be a good boy and stay with your Aunt Cass for a few hours, right?"

Tadashi narrowed his eyes at his parents before wordlessly going to his room, slamming the door. He collapsed onto his bed, glaring at the ceiling.

It wasn't fair! They'd promised him! He'd been waiting for months for this! And now they were breaking his promise because some doctors were obsessed with his super smart little brother.

Half an hour later, when Aunt Cass had arrived and his parents said bye, Tadashi refused to talk to them, still very angry at the broken promise.

After another hour of playing games with his aunt, Tadashi realized that he was being pretty childish. He was still mad though. But he figured he would apologize to his parents when they came back with Hiro.

But when Aunt Cass answered the phone, dropping her mug of coffee and letting out a scream at whatever she had heard, Tadashi knew…

He knew his world had changed.

They had driven in rainy weather before. It wasn't anything new. And it wasn't even heavy rain. But, sometimes, things happen. It was just chance that caused the car to skid out of control. Just chance that the impact killed Tomeo and Marie Hamada instantly.

Just chance that Hiro Hamada had miraculously survived with just a few cuts and bruises.

Tadashi's sobbing managed to drown out Hiro's as the nine year old clung to his baby brother in the hallway of the hospital, their Aunt Cass wrapping her arms around her nephews.

It was all just chance, a small twist of fate.

And now Tadashi and Hiro Hamada were orphans.

Despite all the crying he had done for days and days, Tadashi was very calm throughout the funeral. Hiro, on the other hand, wouldn't stop crying and asking for his parents.

After the services were done, Tadashi had spent some time alone in his room, the shades pulled down. He was still dressed in the crisp black suit he wore to the funeral.

In his hands was a picture of him, his brother, and their parents from just a few months earlier.

It wasn't fair…None of this was fair.

Was this his punishment? Because he had been a brat to his parents about the expo his punishment was to lose them? He should've never gotten mad. It was just one stupid little expo. There would've been more he could've attended. He probably would've gotten more chances to meet Robert Callaghan.

He hadn't even said goodbye to his parents that day. Just stayed stubbornly silent, not even hugging them. They died with their last memory of Tadashi being him acting like a jerk.

Tadashi gritted his teeth, trying his hardest not to start sobbing once again.

It was another's crying that got his attention. Silently, Tadashi left his room and saw Aunt Cass trying to calm down a still sobbing Hiro.

"There, there, Hiro," Aunt Cass shushed as she rocked him, "I'm here…"

"Let me take him, Aunt Cass," Tadashi said, holding out his arms for the boy.

"Oh, sweetie, it's okay, I don't-"

"I can handle it."

After a moment, Aunt Cass handed the three year old over. Tadashi held Hiro close as he returned to his bedroom, taking a seat on the bed.

"I want Mommy and Daddy," Hiro wept.

"…Me too," Tadashi whispered.

"Where are they?"

"They're…away, Hiro. Aunt Cass will look after us now. You love Aunt Cass, right?"

Hiro clung to him tighter, his crying getting softer.

"Tadashi…You won't leave, right?"

Tadashi wrapped his arms even tighter around Hiro, burying his face in his brother's hair.

"No, I won't. It's you and me now, Hiro."

Him and Hiro. He would have to take his job as big brother even more seriously than ever.

It was the only way he would ever make it up to his parents.

And done! Long first chapter, huh? By the way, in the original Big Hero 6 comics, Hiro Takachiho's parents are named Tomeo and Maemi. For this Hiro, I kept the Dad's name but changed up Mom's, since Hiro Hamada is mixed race. Also, the thing about Hiro solving the math problems is based off a scene from the Big Hero 6 manga.

This was just the opening chapter too. There's more to the story. I think I'll have one more chapter of events before the movie timeline. And then we get into the movie timeline. And that's when the AU part of this story kicks in.

I hope you enjoyed this chapter! Please read and review!