The harbor of Kurogane vanished behind them without ceremony.
There was no cheer, no farewell cry, no dramatic horn to mark the crossing. The ship simply moved—slowly at first, then with growing certainty—as if the sea itself had accepted its presence.
Raizen stood at the upper deck, hands resting lightly against the rail, watching the golden spires of the kingdom shrink into the morning haze. The wind pressed against his clothes, cool and steady, carrying the scent of salt and iron.
A year and a half.
The thought settled into him like weight, not fear.
Aoi stood a short distance away, her cloak drawn tight against the breeze. The faint scar across her face caught the early light, neither hidden nor emphasized—simply there, as it always was. She wasn't looking back at the kingdom. Her eyes followed the water ahead.
Senji emerged from below deck, a folded schematic tucked under his arm, expression caught somewhere between curiosity and restrained excitement.
"So," he said, adjusting his gloves, "you feel it yet?"
Aoi glanced sideways. "Feel what?"
Senji tapped the rail with his knuckle. The sound echoed—hollow.
"This isn't just a ship."
⸻
The Descent
They were escorted below deck shortly after sunrise.
The stairway alone told the story.
It did not descend into darkness. Lanterns lined the walls, their glow warm and steady, revealing corridors that stretched far beyond what the ship's exterior suggested. The deeper they went, the wider the passage became, until the air itself changed—less salt, more smoke, spice, oil.
Aoi slowed unconsciously.
"…This is impossible," she murmured.
They stepped into an open concourse.
Beneath the hull of the ship existed a city.
Not a metaphor. Not an exaggeration.
Stone-laid walkways curved gently with the ship's structure, lined with stalls, workshops, and resting quarters stacked in tiers. Fabric awnings fluttered gently despite the enclosed space. Voices overlapped—bartering, laughing, arguing. Children ran past with wooden practice swords, chased by an exasperated woman carrying bundles of cloth.
Above them, the hull arched like a black sky.
Below them, lanternlight reflected off polished metal floors.
Raizen stood still, absorbing it.
"How many people?" he asked.
"Hard to say," Senji replied, eyes already scanning. "Thousands, at least. Maybe more when fully supplied."
Aoi exhaled slowly. "So this is how they cross oceans."
"No," Senji corrected. "This is how they survive them."
⸻
A Marketplace at Sea
They were guided into the central trade quarter.
It felt disturbingly familiar—like any large city market—except for the subtle sway beneath their feet and the constant hum of water moving just beyond the walls.
Clothing stalls dominated one wing.
A merchant with an overly enthusiastic grin waved them over. "First voyage?" he asked, already pulling garments from a rack. "You'll want layers. Sea cold is cruel. Sun worse. Storms worst of all."
Aoi examined a sleeveless travel coat, testing the fabric between her fingers. "Flexible."
"Reinforced thread," the merchant said proudly. "Won't tangle with movement techniques."
She raised a brow, unimpressed but intrigued.
Raizen picked up a simple dark tunic. Plain. Durable. No ornament.
"That's it?" Senji asked.
"It works," Raizen replied.
Aoi glanced at him. "You don't care how you look at all, do you?"
Raizen paused. "Should I?"
She stared at him for a moment, then shook her head. "No. That would be worse."
Senji snorted.
Light laughter followed—brief, unguarded. Rare.
They continued browsing.
Aoi eventually selected attire that balanced mobility and warmth, the cut practical but clean. As she adjusted the collar, Raizen noticed the way her scar softened slightly when she smiled at a passing child.
He almost asked about it.
Almost.
⸻
Whispers of the Kuroshio
They stopped at a food stall, bowls of steaming broth pressed into their hands.
Nearby, sailors spoke in low voices.
"—third ship this year."
"No wreckage?"
"None. Just gone."
Aoi's grip tightened around her bowl.
Another voice whispered, "They say the sea opens there. Like a mouth."
Senji listened without turning his head, memorizing cadence, accent, fear.
Raizen stared into the broth, watching the surface ripple with the ship's movement.
Shinkai no Kuni.
Sunken Realm.
A place people feared enough to mythologize.
⸻
The Offer of Training
Later that day, an official approached them—crisp uniform, posture sharp.
"You are authorized for ship-based training," he said, presenting a slate etched with schedules and insignia. "Participation is optional but recommended."
Senji took it eagerly. "I'll need access to the engineering bay and signal rooms."
"Granted."
Aoi scanned the list. "Movement halls?"
"Yes."
Raizen read silently.
Strategy simulations. Adaptation drills. Multi-opponent analysis.
He nodded once. "I'll attend."
The official bowed. "Your voyage begins now."
⸻
Night Beneath the Hull
That evening, the lanterns dimmed to a softer glow.
The city beneath the ship quieted, though it never fully slept. Raizen stood alone near a reinforced viewing panel where thick crystal revealed the ocean sliding past only a few arm-lengths away.
The water was darker here.
Deeper.
Aoi joined him, her presence announced only by the faint shift of air.
"It feels strange," she said. "Moving so far without walking."
Raizen nodded. "Feels like being carried into something we can't turn back from."
She leaned beside him, close enough that their sleeves brushed.
After a moment, she spoke again. "When this ends… we won't be the same."
Raizen didn't deny it.
"Then we learn who we become," he said quietly.
Far below, something massive passed through the darkness.
Neither of them saw it.
But the water shuddered.