The first sign something was wrong wasn't visual.
It was sound.
A low, subsonic groan rolled through the hull—too deep to be heard properly, more felt than perceived. The submarine's metal frame vibrated, not violently, but with a slow, uneasy rhythm, like the ocean itself had drawn a breath.
Karl straightened immediately. "Agnes."
"I feel it," she said, her glow sharpening as sensor data bloomed around her. "That isn't tectonic drift."
Outside the viewport, the darkness shifted.
The seabed ahead—once solid stone—split.
Not a crack. Not a collapse.
A fissure.
The ocean floor peeled apart like a wound reopening, rock grinding against rock as a trench tore itself wider, exhaling clouds of black silt that swallowed the sub's lights. The pressure spiked suddenly, numbers ticking upward on Karl's HUD.
"…That's new," he muttered.
Agnes's voice dropped, focused, alert. "These aren't natural fractures. They're reactive. Something below is forcing them open."
Another tremor ran through the hull.
Then the trench moved.
From the fissure, shapes began to emerge—slow at first, then deliberate. Massive silhouettes dragged themselves free of the stone, shedding debris like molting armor.
Agnes's tone sharpened. "Karl. We have contact."
The lights caught the first one fully as it hauled itself upward on clawed, anchor-like limbs.
It looked like a shipwreck that had learned how to crawl.
Iron-plated limbs dug into the seabed, pulling an enormous body forward—ribbed with corroded metal, barnacle growth fused into armor. Chains, actual chains, were embedded into its flesh, dragging behind it like vestigial tails.
"Oh no," Karl breathed. "Nope. Don't like that."
"Iron Trawler," Agnes said immediately. "Ocean-floor crawler. Extreme mass. It's anchoring itself to the trench."
As if on cue, the creature pulled.
The submarine lurched downward as an invisible force grabbed hold of the reinforced hull. Alarms flared—pressure, drag, anomalous force vectors.
Karl swore, nanites flaring instinctively as he reinforced the hull. "It's trying to drag us down."
"Yes," Agnes confirmed. "They consume pressure gradients and metal structures. If it reaches full grip—"
"I get it," Karl snapped, pushing power to the thrusters. "We're lunch."
Before he could maneuver away, the water around them darkened.
From the widening fissures poured smaller shapes—hundreds of them—like a living tide. Thin, semi-translucent bodies twisted through the water, each one little more than a membrane wrapped around gnashing maws.
Agnes's voice went cold. "Floodveil Brood."
The swarm hit the hull like rain.
Not impact—adhesion.
They plastered themselves across the sub's exterior, bodies flattening, merging, multiplying. Water displacement readings spiked as they clogged vents, intakes, seams.
"They're breeding on contact," Agnes warned. "They drown cities by sealing infrastructure silently."
Karl clenched his jaw. "Of course they do."
A sudden shriek cut through the water—high, metallic, reverberating through the trench.
Something else emerged.
Tall. Upright.
A figure plated in abyssal armor, its silhouette disturbingly humanoid. Rust-black pauldrons curved like ship hulls, and its head was crowned with jagged protrusions resembling broken masts.
In its hands, it carried a corroded lance that bled dark foam into the water.
Agnes went very still.
"…Dread Mariner," she said quietly. "Deep-sea siege demon."
The creature turned its head.
And looked at the submarine.
The water around it began to fizz.
"Hull integrity degrading," Agnes snapped, suddenly all business. "Corrosive field active. It's targeting stress points."
Karl felt it—nanites sizzling, layers thinning faster than they should. "That thing eats ships."
"Yes," Agnes said. "And it enjoys it."
Another movement—faster this time.
From a side fissure burst a creature shaped like a living battering ram. Its body was encased in layered armor plates, jaws opening far wider than physics should allow.
It lunged—
—and swallowed one of Karl's nanite blasters whole as he fired through an external port.
The weapon vanished into its throat.
A moment later, the demon vomited molten slag, glowing orange as it dispersed into the water.
Karl stared. "…Did it just—"
"Maw Paladin," Agnes said tightly. "Heavily armored devourer. Do not feed it weapons."
"Noted!" Karl barked.
The Iron Trawler pulled again.
The submarine groaned as it was dragged closer to the trench mouth, Floodveil Brood thickening around the hull, their bodies pulsing as they multiplied.
Agnes's hands clenched at her sides. "Conventional nanite weaponry is ineffective underwater. Energy dispersion is too high. Corrosion fields are disrupting cohesion."
"So what," Karl growled, forcing power through the thrusters, "we're just stuck?"
"No," Agnes said—then stopped.
Her glow flickered.
She looked at the trench.
At the pressure readings.
At the Iron Trawler anchoring itself below.
"…Karl," she said slowly, a dangerous edge creeping into her voice. "How much more pressure can the sub take if you reinforce it continuously?"
He glanced at the numbers, then smirked grimly. "More than they can."
Agnes's eyes lit up.
"Good," she said. "Then we don't fight them."
The Dread Mariner raised its lance, corrosive energy spiraling.
"We drown them," Agnes finished.
Karl understood instantly.
He cut forward thrust.
Redirected power downward.
Nanites surged, reinforcing every seam, every joint, every vulnerable plate as Agnes began rerouting ballast systems manually, overriding safety limits.
"Agnes," Karl said, steady but sharp, "if we misjudge this—"
"We won't," she replied fiercely. "They're adapted to depth, not sudden pressure spikes. The trench is unstable. If we force a dive—"
"The pressure gradient will spike hard enough to liquefy anything not fully abyssal," Karl finished.
"Exactly."
The Iron Trawler sensed the shift and pulled harder.
"Too late," Karl muttered.
He dumped ballast.
The submarine dropped.
Water screamed past the hull as depth increased violently—pressure slamming into them like a descending wall. Agnes braced herself against the console, voice tight but controlled as she managed the descent.
Outside—
The Floodveil Brood burst.
Their bodies collapsed inward, membranes imploding as pressure crushed them instantly. The Maw Paladin convulsed, armor plates cracking as its own swallowed slag detonated inside it.
The Dread Mariner tried to retreat—
—but the pressure caught it mid-motion.
Its armor folded.
Its lance snapped.
The corrosive field flickered, then vanished as the demon was compressed into a twisted, sinking wreck.
The Iron Trawler roared—a deep, seismic sound—as its anchors tore free of the trench. Its massive body cracked, pressure overwhelming even its abyss-forged bulk.
It imploded in slow, horrifying silence.
Karl exhaled shakily as the pressure readings stabilized.
Agnes rerouted systems with trembling precision, then eased the dive just enough—
—and angled them forward.
Ahead, a narrow underwater ravine opened like a scar, twisting sharply through the rock.
"Ravine passage detected," Agnes said, breathless but triumphant. "Tight fit."
Karl grinned despite himself. "My favorite kind."
He threaded the submarine into the ravine just as the last remnants of the demons were crushed and scattered behind them. Stone walls closed in, shielding them from the open trench as the ocean's pressure settled back into something survivable.
For a moment—
Only silence.
Then Karl laughed—a short, incredulous sound. "We just used the ocean as a weapon."
Agnes drifted closer, her glow softening again, exhaustion and exhilaration mixing in her expression. "You reinforced reality and aimed it downward."
He glanced at her. "You're proud."
"I am," she admitted. "And a little terrified."
"Same."
The ravine carried them forward, away from the fissures, away from the demons, deeper into the Pacific's dark arteries.
Behind them, the trench closed slowly.
Like it had never opened at all.