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San Fransokyo Year 2100

Summary:

So, I just had a remarkable idea of placing Big Hero 6 universe in year 2100 with awesome inventions.
Also to be noted Tadashi Hamada lives in this AU. Obake is Professor Aken and he doesn't turn out a villain after the amplifier incident. Also to be noted Callaghan's daughter never ended up in a portal so no Kabuki mask guy just an average yet grumpy Professor.
Baymax the huggable detective is a must for this AU. I made him more enjoyable with Mochi having a translation collar which let her speak in English to her owners. (Adorable)

Notes:

I might post chapter every week. To be noted the working title is still under discussion I would give it a suitable one soon. So anyone has any suggestions then I all ears on altering the work title

Chapter Text

Chapter 1 — The City That Never Sleeps, Just Upgrades
Morning sunlight refracted off the glass veins of San Fransokyo, breaking into a thousand holographic shards that danced across the café windows. Above the skyline, sky-lanes buzzed with flying cars, gliding like metallic koi through invisible currents. The city pulsed in rhythm — efficient, beautiful, a living organism made of circuitry and chlorophyll.
Inside the Lucky Cat Café, the hum was calmer but no less alive. Holographic menus shimmered above each table, adjusting to customers’ eye movements. A stream of water spiraled mid-air through the shop — a ribbon of floating liquid held aloft by magnetic current. Within it drifted real flowers, their petals bright as neon jellyfish. The stream circled the café like a lazy halo before vanishing through a gravity sink in the ceiling.
Behind the counter, Aunt Cass was multitasking with her usual high-speed grace — one hand stirring a pan that sizzled on an induction slab, the other tapping holographic orders hovering beside her face. Mochi, now fitted with a sleek translation collar, sat proudly on the counter, tail swishing like a metronome.
“Hungry,” the collar chirped in a tinny, robotic tone.
“Feed me. Feed me now.”
“Kittens look sad.”
Tadashi exhaled. “You’re not wrong, Mochi.”
Across from him sat Hiro, head bowed over a steaming cup of synth-coffee, his expression somewhere between guilt and defiance. The faint bruise on his cheek still glowed where a security drone’s stun beam had grazed him the night before.
“Do you even realize how lucky you are?” Tadashi’s voice was calm, but the restraint in it made Hiro wince harder than shouting would’ve. “If I hadn’t gotten there when I did, the militia would’ve hauled you to the juvenile sector. And Good Alley isn’t exactly a place they let kids walk out of.”
Hiro muttered, “They weren’t supposed to catch me. My bot was winning until—”
“Until it exploded,” Tadashi cut in. “Because you overloaded its neural grid to make it faster. You’re thirteen, Hiro. You’re not supposed to even know how to hack a combat model.”
Hiro looked up, eyes sparking. “You think those people down there fight for fun? They do it to survive! I just wanted to see how they make their bots adaptive with scrap tech — it’s genius!”
Tadashi rubbed his forehead, frustration warring with reluctant admiration. His kid brother’s mind was brilliant, reckless, and way too curious for his own good.
Outside the café’s transparent wall, the districts stretched in layers like an enormous circuit board. Tadashi gestured toward them.
“Look, you see that skyline? Each sector’s got its own rhythm. Administrative on top — all drones and holograms. Then the research towers, where Callaghan runs SFIT. The laborers work beneath the forest canopies. Every layer connects because it’s supposed to. You step out of line in one, the whole system stutters.”
Hiro stared out the window. Flying cars threaded between the spires. Far below, a glimmer of neon marked where Good Alley hid under the canopy’s shadow.
“Maybe the system deserves a stutter,” he murmured.
Tadashi sighed. “That kind of thinking gets people hurt. There’s a reason we have districts — order keeps chaos from swallowing the city.”
Mochi’s collar purred, “Chaos tastes like fish.”
Aunt Cass laughed from the kitchen. “See, even Mochi thinks you’re overreacting, Tadashi!”
But Tadashi wasn’t smiling. He looked back at Hiro — the same wild curiosity in his eyes that he’d once seen in Professor Callaghan’s old students. The kind that could save the world… or accidentally burn a hole through it.
He lowered his voice. “I’m not trying to stop you, Hiro. I just don’t want to see you end up like some of the engineers who thought they could outsmart the city’s limits.”
“Like Bob Aken?” Hiro asked quietly.
Tadashi hesitated. “Yeah. Like him.”
The café’s floating stream gave a low hum as magnetic current shifted, sending a ring of petals swirling past their table — soft, glowing, ephemeral. Tadashi watched them drift, then added, “Promise me, no more Good Alley. Not until you’re ready to face what really goes on down there.”
Hiro didn’t answer. He just reached out and caught one of the petals before it floated away, its veins glowing faintly against his palm.
Outside, San Fransokyo gleamed — perfect, serene, and just beneath the surface, humming with secrets waiting to be found.
“Kittens need breakfast,” Mochi declared solemnly.
“And rules. Maybe snacks first.”
Tadashi finally cracked a smile. “Snacks first,” he said, glancing at Hiro. “Then rules.”