A/N: So, this is all thanks to the wonderful Big Sis AU suggested by appleye over on tumblr. It also marks my first multi-chaptered fic for the Big Hero 6 fandom. I'm really excited about this, guys! Please let me know what you think, and you can also interact with me over on tumblr (url is amillion-smiles) :)

Prologue: The Starting Line

There were bad ideas, and then there were Bad Ideas.

Hiro, it seemed, was awfully good at getting involved with the latter. Geniuses or not, twelve-year-olds had no place on San Fransokyo's streets during the nighttime, a fact made more glaringly obvious by the glint of Yama's grin as he and his goons advanced.

"Look guys, I'm sure we can work something out…" Hiro trailed off nervously, wincing as the back of his sneaker scraped against the concrete wall behind him. The wad of cash he'd won crinkled in the pocket of his hoodie as he held Happy, his bot, closer to his chest, eyes darting around the alley.

He needed space. With enough range and his remote controller, Hiro could make short work of these guys, but Happy wasn't built for close contact. Neither, cringed Hiro, was he. He figured he could take about two punches before he'd be saying sayonara to his two front teeth, among other things.

Goodbye, world. It's been fun.

"Lights out, Zero," said Yama, his arm rearing back.

Hiro closed his eyes. Braced himself.

And ducked.

"YARGH!" bellowed Yama as his fist collided with the concrete. Hiro blinked at the massive man's arm in amazement before survival instincts took over. He darted around Yama's stunned bulk, evading the grasping arms of Yama's friends.

I can't believe that worked…those idiots—

The laugh bubbling up in his throat was quickly choked off as someone grabbed his hood, yanking him to a stop.

Well, shit.

Unbidden, an image of Tadashi appeared in Hiro's mind, his brow puckered in disappointment as he scolded, "No cursing, Hiro." But Tadashi wasn't here to chastise him or bail him out. Hiro kicked at his captors, legs flailing uselessly as he was dragged upwards so that his feet no longer touched the ground. Someone pinned his arms close to his side as Yama advanced, looking more feral than ever.

"Nobody gets away from me," he enunciated, punctuating his threat with a sharp jab to Hiro's chest. The reddened skin of his knuckles stood out under the moonlight.

Hiro squirmed. If this was what staring death in the face felt like, he didn't like it one bit, and Yama's putrid breath was the only thing distracting Hiro from the fact that things had stopped being a laughing matter the minute he'd left the club. If there was one thing he had learned from his nighttime escapades, it was that you could root for the underdog all you wanted, but the minute you were outside the bot-fighting ring? You bet on the big guy.

To distract himself from his impending fate, Hiro looked up at the sky, choosing to fixate on the scattering of stars. They seemed brighter tonight. Perfect for a final prayer.

I'll do whatever you want. I'll give up gummy bears and Aunt Cass's hot wings—just please, please get me out of this alive.

He held his breath. Maybe if he passed out, it wouldn't hurt as much; there was always that hope.

And then, out of nowhere: a roar.

It was the most glorious sound Hiro had ever heard. Above him, the sky became blotted out by the dark silhouette of a motorbike descending from the clouds like some avenging angel. Yama and his men scattered to avoid being flattened, dropping Hiro in their desperation to get away. He fell to his knees, coughing, barely regaining his breath before the black-clad rider hoisted him onto the motorbike, revved the engine, and sped.

"Whoa, whoa, whoa!" yelped Hiro, throwing his arms around the rider to prevent from falling off the back end of the vehicle. He hadn't escaped from getting smashed in the face only to become a skid mark in the middle of the street, anyways. Tadashi was probably turning over in his sleep right now—hopping on some stranger's motorbike, Hiro? Really?—but Hiro couldn't find it in himself to care; he was too relieved.

Besides, it was kind of exhilarating. This rider obviously knew what he was doing, weaving in and out of traffic without a care in the world. He was small, Hiro noticed, but it made him seem more sleek and streamlined as he hunched over the handlebars.

They pulled to a stop at the corner right before one of the busier streets. Hiro took his cue, sliding off the bike and hopping onto the sidewalk.

"Thanks, ma—woman," he corrected quickly as his savior removed her helmet, revealing a shock of black hair streaked with purple and a pair of defiant eyes outlined by black eyeliner and pale purple eyeshadow.

"You okay?" she asked, raking a hand through her short hair.

He was more than okay. He was—

"That was awesome!" gushed Hiro. "I've never seen anyone drive like that—and where'd you get these wheels?" He got closer to the curb, nearly falling over as he bent his neck to inspect the tire treads.

The girl snorted, but the way she leaned protectively against her bike told Hiro that she was pleased with his compliment. "What are you—ten?"

"Twelve," he corrected, undaunted by her tone.

"Still way too young to be getting involved with Yama and his buffoons."

"You know them?"

She rolled her eyes, a burst of pink squeezing past her lips as she exhaled a bubble of gum. "Everyone from my part of town does."

"Oh. Well, thanks for saving me from them."

"You have anywhere to go?"

"Yeah. My brother's probably awake by now, so he should find me—"

"Hiro!" called a frantic voice as several cars honked, and Hiro caught sight of a red moped approaching from farther down the street.

"And that would be him."

Satisfied that Hiro was now in better hands, the girl pulled her helmet back over her head and slung a leg over the side of her bike. She waited, poised at the edge of the curb, until Tadashi pulled completely into view, face red from a mixture of exertion and panic. His shirt was on inside-out, and Hiro felt slightly embarrassed on his behalf, especially when he compared Tadashi's dingy moped to the girl's jet-black beast of a ride.

Hiro wanted one really, really badly.

Tadashi's face loomed into view, interrupting Hiro's fantasy. "Hiro Hamada," he thundered, shaking Hiro by the shoulders, "what on earth were you thinking, sneaking off like that—are you hurt? Did you break anything? Are you even listening to me?"

"Bye!" Hiro called, watching the girl peel away from the sidewalk. She raised her hand in a two-fingered salute as she disappeared.

Exasperated, Tadashi made sure she was gone before turning back to Hiro and flicking the side of his head. "Knucklehead. You're grounded, do you hear me?"

Driving that thing probably feels like flying, Hiro thought instead.

"Yeah, yeah."

o.O.o

It wasn't that Hiro didn't learn from his mistakes. It was just that quick cash and the thrill of winning spoke louder than his common sense these days.

He'd honored Tadashi's week-long moratorium, but that just meant that he and Happy, now free, were itching for a good fight. Hiro had purposely picked a lesser-known arena tonight, one where he knew Yama wouldn't be. Besides, with the space of a week between them, his earlier encounter with Yama seemed less frightening and more like the kind of story you told your cafeteria buddies, complete with sound effects.

So he left the club that night with full confidence that he would get home in one piece.

And promptly ran straight into someone.

"Watch where you're going, kid," said a silky voice, and Hiro looked up to find white teeth glimmering sharply in the darkness.

If Yama reminded him of a rhino, this man reminded Hiro of a snake—lean and coiled and sharpened finesse. He had a cigarette clamped between his teeth and regarded Hiro coolly through lidded eyes.

Hiro's blood slowed and he took a tiny, hesitant step backwards.

The man's smile widened. He snapped his fingers, extending a hand. "Hey, I know. How about we make a deal—"

The sound of an engine cut him off. Twin headlights cut through the gloom.

"Sorry, but this one's mine," said a voice, clipped but clear, before Hiro found himself hauled away.

He was better prepared this time and wasted no time wrapping his arms around the rider's waist. The wind made his eyes water, but Hiro raised his voice above the air rushing past his ears to greet, "Hey, it's you again!"

"Don't sound so excited," she grunted, veering left.

o.O.o

"So do you have a death wish or are you just stupid?"

Hiro was starting to lose track, but he was pretty sure this was their fifth time meeting. Or the fifth time he'd escaped by the skin of his teeth, if you wanted to be a pessimist about it.

"Wow, you don't pull any punches," he said, tightening his grip as they accelerated through the intersection just before the light transitioned to red.

"Woman up."

Hiro stayed silent, pondering. "Hey, so, do you have a name or something…?"

"GoGo."

"GoGo," Hiro repeated. "That's really—" he waited until they had pulled to a stop, "—fitting."

She pulled her helmet off and swiveled to face him, smirking. "Really."

"Really." He scrambled off, making sure nothing had fallen out of his pockets. "I'm—"

"Hiro."

"Yeah. Wait, how'd you know—oh, right, that one time with Tadashi."

GoGo tilted her head. "Do you not get along with your brother?"

Hiro blinked. "No. We're pretty close, actually. What makes you think otherwise?"

"I can't imagine he'd be very happy with this." She gestured to their surroundings: graffitied walls, an overflowing dumpster, the dim flicker of a streetlight and the flyers peeling off a telephone pole.

"That's because he thinks I'm going to get myself hurt or locked up."

"With good reason."

"Well, yeah. But now he doesn't have to worry, because I've got someone like you to bail me out. I mean, you've saved me five times in a row now. What are the odds of that? It's almost like you're watching out for me or something."

GoGo stiffened, glaring. "I'm not your nanny."

"No, but…" Hiro trailed off, an idea taking shape. "Have you ever been to a bot fight?"

"Heard of them."

"Do you want to go to one?"

GoGo crossed her arms. "Get to the point."

"I was just thinking that you don't look like someone people would want to mess with. So, like, if you accompanied me to these things, maybe I'd stop getting cornered afterwards. And then that saves you the trouble of sweeping in and grabbing me." When GoGo didn't look convinced, Hiro added, "I could pay you or something. Like a security detail."

GoGo pursed her lips, blowing a bubble. "How much?"

"Um…like, ten dollars?"

GoGo raised an eyebrow.

"Okay, twenty."

Nodding, GoGo held out a hand; the fabric of her fingerless gloves rubbed against Hiro's palm as he took it and shook, firmly.

"Deal."

o.O.o

Knowing that there was at least one person in the room not out to get him was a big confidence booster. Hiro walked out of the bot-fighting arena that night with nearly three hundred dollars of prize money.

"Man do I wish this was legal," he said, reveling in the sound of the bills slapping together as he waved them in the air.

"The law ain't gonna save you from this," someone sneered, detaching himself from where he'd been leaning against the side of the dumpster. He was wearing an oversized Hawaiian-print shirt and had a hunched way of walking, his hands shoved in his jean pockets as if he had all the time in the world. Two figures joined him, and Hiro internally groaned. Greasy-haired Gabe and the Bandana Brothers. He'd heard about them: slow, liked to talk big. Nothing to worry about unless you were outnumbered three to one and half their size.

He snuck a glance over his shoulder, stomach dropping when he realized that GoGo was nowhere to be found. Stupid. He'd been so caught up in his winnings that he hadn't bothered to check if she'd actually followed him when he left. She hadn't collected her payment yet, but Hiro knew that if he'd had to choose between twenty dollars and getting away from a sticky situation in one piece, he'd definitely have picked the latter.

He swallowed, returning his gaze to Greasy-haired Gabe. "Um, so—"

"What's the hold-up, Hiro?"

Hiro breathed a sigh of relief, turning to see GoGo leaning against the doorway, something silver swinging from her hand. His eyes widened. Holy crap, when did she get a wrench?

"GoGo?" blurted one of the Bandana Brothers, squinting as if he couldn't quite believe it.

"Jeff," GoGo acknowledged curtly, walking down the stairs to stand beside Hiro, her arms folded across her chest. "Mind telling me why you're giving my brother a hard time?"

"I didn't know you had a brother," said Greasy-haired Gabe, frowning.

GoGo laughed, but there was something dry about it. Hiro wondered what her real laugh sounded like. "I try to forget about it sometimes, too," she said, slinging an arm around Hiro's neck in a gesture of familiarity. "Tried to keep him out of the circuit for as long as I could, but I guess it runs in the family." She shrugged, the wrench tapping against her thigh. "You guys headed somewhere?"

"Yes," swallowed Greasy-haired Gabe, looking suddenly uncomfortable. "We were just about to leave."

He and the Bandana Brothers backpedaled before turning their backs to Hiro and GoGo completely and slinking away. Hiro watched them go, his heart thumping in his chest, before he shifted slightly to regard GoGo out of the corner of his eye. Her face was impassive in the moonlight.

"They knew you," remarked Hiro once he was sure that they were completely alone.

GoGo shrugged, stepping away from him. "A lot of people do."

"But you don't go to bot fights."

"There's more to do in the Dragon District than bot-fight, Hiro."

His interest was piqued, now. He followed GoGo to her bike, asking, "Like what?"

"I'll tell you some other time. Just get on the bike."

"All right, all right. Whatever you say…big sis," grinned Hiro, unable to resist the opportunity.

GoGo paused. For a tense moment, Hiro thought she was going to punch him.

Instead, she reached over and shoved his head slightly, ruffling his hair.

"Watch it," she warned.

o.O.o

"This is a restaurant," said Hiro, staring up at the ruby red eyes of the metal dragon perched above the entrance.

"Good job, genius," said GoGo, parking her bike. Hiro watched her lock it. She was in a good mood today, as close to "bouncy" as Hiro imagined GoGo could ever be. Pride seemed to radiate off her, and she held her head higher, her shoulders more upright. "What do you feel like eating?"

"I don't have any money," he said, scrambling to catch up. For someone with such short legs, GoGo walked fast.

"But I do." GoGo stuck a crisp fifty-dollar bill in Hiro's face.

"Whoa, sweet," Hiro said, making a grab for it at the same time GoGo yanked it out of reach, shoving it back into the folds of her leather jacket. "Where'd you get that?"

She flashed him an enigmatic smile. "You've got your ways, I've got mine."

"Come on," whined Hiro, but any other words he had died in his throat as GoGo pushed open the doors of the restaurant.

It smelled heavenly. Like duck fat and steamed lotus buns, and Hiro's mouth watered as a server walked by carrying a platter of leafy snow pea shoots. A warm, buttery light diffused through the whole restaurant, and GoGo had to grab his sleeve to get him to keep walking.

They collapsed into a cozy booth tucked out of the way. The stuffing was a little ripped, and the silverware seemed a bit tarnished, but Hiro overlooked all of these things the minute the menu arrived.

"Oh man," he groaned, eyes scanning his options, "I don't know where to begin."

GoGo smirked, one elbow resting along the top of the booth, raising her other hand to flag down a waiter. "I do."

o.O.o

Hiro was stuffed. About to explode. He couldn't eat another—well, maybe one more dumpling.

GoGo rolled her eyes as Hiro reached for the last dumpling on the plate before sagging back against the seat.

"Mmph," he groaned. "These are amazing."

Guiltily, he realized that he hadn't even thought to ask GoGo before grabbing the last piece of food. She didn't seem to mind, though. Rather, she was playing with the straw of her drink, looking thoughtful.

"Hey, GoGo?"

GoGo's eyes flickered up.

"Do you actually have any siblings?"

GoGo looked surprised, mouth dropping open slightly before she closed it tightly and shook her head. "No."

"Do you want any?"

"Sometimes." A teasing spark entered her eyes. "If I had a brother, though, he'd never sneak out on my watch."

Hiro shrugged. "What Tadashi doesn't know won't hurt him."

"How do you manage it, anyways? Sleeping pills?"

"Nah," said Hiro, taking Happy out and playing with its components. "Tadashi's just been really busy at school working on his project, so when he gets home he's usually out cold."

GoGo's eyes narrowed. "When do you sleep, if you're running around town all night?"

"In class." And then, because he couldn't stand the disappointment blooming on GoGo's face, for some reason, he added, "I still get good grades, though!"

"Right."

"Honest! I'll bring my report card some time as proof."

"Okay, Hiro," said GoGo, cracking a smile. "Let's get you home."

"Hey, what—" spluttered Hiro, practically falling out of the booth as he rushed to follow GoGo, "what's with you treating me like a little kid all of a sudden?"

"You are a little kid."

"Not that little."

"I'm six years older. Trust me, you're little."

"Blah blah blah," grumbled Hiro, clambering on behind GoGo as they got ready to pull out of the lot. "Hey, you want to know something that just occurred to me?"

"What?" asked GoGo, her voice muffled by the helmet.

"Isn't it kind of dangerous for me to be riding this without a helmet? I mean, I could fall off and crack my head open or something."

He could almost hear her smirking. "Since when did you care about safety rules, Hiro?"

"Since, like, three seconds ago," said Hiro as they joined the flow of traffic. "Honestly, though, that might be something to think about. It'd be a good investment."

"What makes you so sure I want you sticking around?"

"Are you kidding me? I'm awesome. You obviously want me sticking around," said Hiro, gaining momentum as he spoke. "You wouldn't have bought me dinner if you didn't."

There was a long pause as they waited for the light to turn green, and Hiro wondered if he'd overstepped some invisible line. But as they started forward again, GoGo murmured, "True."

Something warm spread through his chest at her words. It was different than the feeling he got from bot-fighting; deep down, Hiro knew that GoGo's compassion wasn't something that could be won, only earned. And it felt reassuring, knowing he had it.

He dug his chin into her back, yawning. "Thanks for tonight, GoGo. It was pretty fun."

"More fun than bot-fighting?"

"Not quite. But close."

o.O.o

She'd gotten him a helmet.

Hiro stared, not quite believing his eyes. It was purple, with two red stripes running down the sides, and felt relatively light as he turned it over in his hands, inspecting it.

"Wow, GoGo, I'm…wow."

"Better take good care of it," she said, simply, adjusting her biker gloves.

A sudden thought occurred to Hiro. "Wait, but where am I going to keep it? Tadashi'll see, and then he'll wonder—"

He was cut off by the sound of GoGo's laugh—a real one this time. It wasn't high-pitched or dainty or anything like Hiro had imagined it would be; it was something solid, grounding, like the rest of the world could pass her by and GoGo would still be there, laughing.

"You're a genius, Hiro," she said, the smile not leaving her face. "You'll figure it out."

o.O.o

He needed to get out of here.

The midnight crowd was beginning to filter in, and Hiro was ready to call it quits. One problem, remained, however: GoGo was nowhere to be seen.

They didn't always show up together. GoGo had a life of her own, and Hiro had no problem finding the gambling dens. But he'd gotten used to always leaving with GoGo by his side, the calming, protective air that her presence conferred. In some of the dens, word had spread that he was GoGo's brother, bestowing him with another badge of security. Hiro surmised that GoGo was some sort of underground celebrity, though he hadn't yet figured out what she was famous for, and she hadn't told him of her own accord.

Surreptitiously, he texted her before the next round started: where r u?

"All right, ladies and gentlemen! Taking wagers for Round Two!" the announcer looked at him over her shoulder. "You still in?"

"Yep," said Hiro, sweating in his jacket. Just stay in the ring. As long as he was in the ring, he was safe.

His run was short-lived, however. Hiro couldn't keep his mind from wandering, eyes examining the crowd every so often. A flash of purple caught his attention and he zeroed in on it; by the time he realized it was just one of the roller geisha and returned his gaze to the ring, Happy had been down for the count for too long.

"That's a match!" said the announcer as some members of the audience groaned. "Next challenger?"

Hiro gathered up Happy's remains and his earnings and edged out of the ring, looking for the nearest exit. Most people were vying for a position in the next round, which was good, but there were a few characters toward the back of the room that Hiro didn't like the look of.

He ducked into the bathroom, hoping that any potential pursuers would be thrown off or too impatient to sit around and wait. Heaving a sigh of relief, he locked the door behind him and sunk down onto the grubby tiles, pulling his phone out of his pocket.

Still no response from GoGo.

He checked the time. 11:56. He could wait half an hour…

Half an hour turned into forty minutes and then into fifty. By then, Hiro had played several rounds of San Fransokyo Space Bots on his phone, and the flashing red symbol in the corner warned him that his battery was low. He needed to get home.

Hiro sighed, resting his head against the door and swallowing past the dread in his stomach. When had he become so cowardly? He'd gotten by before without GoGo—he could do so again.

Shoving away any doubts, Hiro cracked the door open slowly, scanning the darkened hallway. He could still hear people hooting and hollering from farther in the building, and he used the noise to mask his departure, cringing when he stepped on a creaky floorboard.

Once he was outside in the courtyard, Hiro sucked in a huge breath, gulping in the musky nighttime—or did it count as early morning, now?—air.

There, that wasn't so hard.

"Well, well, well."

Jumping, Hiro whirled around. Greasy-haired Gabe and the Bandana Brothers were back, and this time their eyes seemed sharper. The lazy edge had disappeared, replaced with a knowing gleam.

"Hello, Hiro," oozed Gabe.

"H-hello," stammered Hiro, trying to stand his ground. He called up an image of GoGo, trying to emulate her stance, the casual posture that promised a world of retribution if you threatened it.

"Where's your sister?"

"Busy."

Greasy-haired Gabe chuckled, one corner of his mouth lifting higher than the other. "Busy with what?"

"I…" I don't know.

"Heard you cleaned up real good in there, Hiro," said Gabe, making a motion behind his back to the brothers. Hiro watched them warily as they peeled away from Gabe's side and began to flank him instead.

"Leave me alone," he said, fighting to keep his voice from trembling. GoGo where are you please I need you please come speeding in on your motorbike please—

"We will," Gabe said smoothly, watching as Hiro started to scramble backwards—too late—and tripped. One of the Bandana Brothers caught him, and Hiro thrashed in his grip, fear clawing its way up from his stomach until he couldn't think of anything else. He'd forgotten how it felt to be alone, really alone, with no way out, and anger and despair collided in his gut in equal measure—he was so helpless and he hated it—

"Easy there, little guy," soothed Gabe, reaching into Hiro's pocket and taking out the cash, and then he was nodding at the Bandana Brothers to let Hiro go and Hiro's knees and hands were hitting the gray stone of the courtyard but all he could see was red—

He charged without thinking, launching himself onto Gabe's back as Gabe turned away. Gabe's surprise was short-lived; in a flash, he threw Hiro off. Hiro gasped as his back made contact with the ground, stunned.

"You little punk!" Gabe was advancing now, the cords of his neck taut with anger, the cloak of nonchalance having vanished. "When I say stay down, you stay down, you hear?" He drew back and kicked Hiro.

The blow sent a sharp flare of pain up Hiro's side and he curled inwards, hissing. Above him, he could make out one of the Bandana Brothers—what had GoGo called him? Jeff?—pulling Gabe away, saying, "He's just a kid, Gabe. Let's go."

"Yeah, run away, Gabe," Hiro taunted, struggling to push himself up with the hand not clutching his side, "You're just a big, stupid coward—"

"I said," hissed Gabe, breaking free of Jeff's grip and stomping towards Hiro, "to stay down."

This time, he went for Hiro's face.

o.O.o

"Hiro? Hiro, god, please wake up…Hiro?"

"Tadashi?" Hiro said weakly, opening his eyes slowly and watching as his brother's face swam into view, hazy and out of focus.

"Right here. I'm—here, can you sit up?" One of Tadashi's arms reached around him, easing him into a sitting position. He could hear police sirens in the distance and wondered, absentmindedly, if they were coming for him. It felt like a car alarm had gone off in his head—there was an incessant throbbing in his temple.

"How bad is it?" he asked, taking note of the way Tadashi bit his lip as he inspected him.

"You're going to have a black eye," said Tadashi, cradling his face. "Other than that, it's hard for me to tell. How do you feel?"

Fine, Hiro wanted to say, but his heart wasn't in it. Scared. Humiliated. And he knew it wasn't fair, but a tiny part of him blamed GoGo, whispering, this wouldn't have happened if she'd been here, except GoGo was gone and maybe he'd never see her again. Definitely, Hiro corrected himself. He'd definitely never see her again, because Tadashi had been right—it was stupid to leave the house and sneak out to bot fights when it all ended up like this, one way or another. People hated you if you knew too much or won too much; they built you up just to let you down.

"Awful," Hiro finally decided, the tears hot and heavy as he finally released his hurt and frustration, sagging forward in Tadashi's arms. "I want—" he took a ragged breath, "I want to go home."

"I know," murmured Tadashi, rubbing circles on Hiro's back, careful not to press against Hiro's swollen eye, "I know."

And Hiro sat and cried and hugged the one person who wouldn't leave him, no matter what.