Hikaru returned to his temporary base of operations.
Tonight's mission had been immensely fruitful, so much so that he decided to halt his current work and take some time to refine the Emerald Grimoire's connection system.
And once that idea crossed his mind, he was already acting on it.
It was late. Chazz didn't seem to have time to drop by, and Hikaru himself was too busy. Before he could dive into his alchemy calculations, he needed to organize his thoughts.
Inside the hideout that Yusei had once used for D-Wheel testing, Hikaru looked up at a massive map pinned to the wall, a complete layout of the City.
At the very bottom of the map, a single mark read "You are here."
That was the current base, the same location Yusei had labeled when he first mapped out the city's underground.
Above that area lay the vast stretch of territory where the lower-class citizens lived, the Underground Sector, or simply "the Ground."
On the left side of that level was the Psychic Research Facility – Eden, the place Hikaru had visited earlier that day.
In contrast, on the upper-right edge of the same layer sat the Detention Center, the local prison.
The nobility of the Upper City despised seeing the "pollution" of the lower class, so they'd exiled both independent institutions like Eden and government prisons to the far outskirts, sealing them off from sight.
This whole layer was known as the Isolation Zone.
The City itself was built as a spiraling tower, a literal structure of hierarchy.
The "Underground Sector" wasn't only a social designation; it was physically beneath everything else.
Technically, there were three ways upward. The first two were the slanted surface paths, like the ones Hikaru had driven today, and then a vertical transit corridor connecting directly to the Upper City.
That last route, however, was heavily guarded by Sector Security.
The last time Hikaru tested his D-Wheel there, that was where he'd been discovered.
When he had driven to the city's edge earlier and looked back, he could see the City like a tilted spire rising toward the heavens, its districts connected by countless looping raceways.
Beyond the lower levels, the architecture rose into a geometric hexagonal pattern, a honeycomb of elevated districts.
If the Underground and Isolation Zones were "restricted areas," then moving higher meant entering the Middle Layer, the Commoner District.
This was the largest region of the City aside from the Underground itself.
Above that resided the true Upper City, home of the aristocrats.
Only a few landmarks on the upper tiers bore names.
At the pinnacle stood the Taiichi Gardens, and to the northeast, just beneath the floating plaza, was the Perpetual Motion Research Institute.
The rest were left blank, anonymous strongholds of privilege.
Hikaru rubbed his chin thoughtfully.
If he numbered the layers, he was now standing on level 10.
Above him was 9, the Lower Sector, then 8- Eden, 7, the Prison, and so on…
A frown creased his brow.
Those numbers… something about them felt strange.
Beside him, Tierra lounged back with her hands folded behind her head. For once, she didn't offer a single comment.
Hikaru studied the map for a long time before shaking his head and forcing himself to stop overthinking. He needed to focus and plan tomorrow's route to the Detention Center.
That place… yes, it rang a bell.
In the original Yu-Gi-Oh! 5D's, the prison had been an important location.
Coincidentally, it also appeared in Arc-V, a recurring "main character prison stop," where heroes inevitably found themselves locked up at least once.
It was always a key story hub, full of hidden connections.
In Arc-V, the underground duelist Chojiro Tokonatsu had been one such inmate, a street duelist who rose to fame by teaching children to Duel instead of fight, earning the affection of the Satellite's poor.
He had come to despise the aristocrats who shouted hollow slogans about "equality" yet never listened to the cries of the Commons.
Hating the way society had been split between classes, Chōjirō challenged duelists from the Upper Sector directly.
In his desperation to win, to claim justice for the downtrodden, he eventually crossed the line.
He cheated. And for that, he was arrested.
A duelist with ideals, but one whose edges had been worn down by the weight of reality.
From what Hikaru had learned of the Synchro Dimension so far, that man should be imprisoned somewhere inside the Detention Center.
If even Sayer had once been drawn into the struggle for the so-called "One True God," then perhaps Chōjirō would soon be involved too.
After all, in the original story he was one of the most pivotal figures in the Synchro arc, no less significant than Shinji.
Having mapped his route, Hikaru uploaded the navigation data into his Duel Disk and began reviewing his Deck.
He hadn't had time to inspect it properly in days, and as he flipped through the cards, something unfamiliar caught his eye.
"Huh? Teleport Fusion."
Hikaru blinked, pulling out a brand-new Fusion Spell.
Another new card.
But since he'd already encountered original cards like Gem-Knight Dispersion, it wasn't entirely shocking.
He examined the effect text carefully.
"During either player's Main Phase: banish Psychic-Type monsters from your field or Graveyard to Fusion Summon one Psychic Fusion Monster."
He nodded slightly.
"Hmm… not bad. A clean banish-based Fusion spell."
The rest of the effect read:
"If a Psychic-Type Fusion Monster you control that was Special Summoned from the Extra Deck is destroyed by battle or card effect: you can banish this card from your GY, then Special Summon one of your banished Psychic monsters."
"Oh, that's actually pretty solid," Hikaru muttered with approval.
It wasn't as astonishing as Gem-Knight Dispersion, but it had its own charm, perfect for combining with the Myutant Ultimus he'd obtained earlier, or even to mix with Metalfoes.
At the very least, it was one more Fusion spell to add to his arsenal.
Unfortunately, his Extra Deck hadn't expanded; apparently his duel with Sayer hadn't earned him a new Fusion Monster, only this spell as a by-product.
Still, Hikaru wasn't greedy. Today's harvest had already far exceeded expectations.
A new Fusion Spell was just a welcome bonus.
The next morning, after an entire night spent experimenting, Hikaru stifled a yawn, mounted his D-Wheel, and set off toward the prison.
He hadn't even made it halfway when...
BOOM!
A massive explosion thundered through the air.
His eyes widened as a blue-black mushroom cloud rose in the distance.
That was the direction of the Detention Center.
"An explosion—!?"