Bill felt the weight of the armament slung at his waist pressed against his outer armor. It was an ancient, perfectly cuboid firearm that looked entirely out of place in this age—a Disintegration Gun. This forbidden relic from the Dark Age of Technology was a trophy he had wrestled from the corpse of a techno-barbarian warlord on Terra, right after he had executed the tyrant with his chainsword. It was a devastating weapon, capable of dissolving any target into a cloud of stray atoms in a heartbeat. However, it was far too volatile and dangerous to be discharged recklessly within the confines of a narrow tunnel.
They were advancing deeper into a subterranean conduit of Neptune. Bill marched alongside the survivors of the 13th Company and remnants of other shattered brotherhoods. Along the endless stretch of the corridor, the oppressive dark and damp chill were broken only by the heavy, rhythmic thuds of armored boots and the hushed whispers of the warriors. They traded dark, gallows humor about death and obliteration—the sole anchor keeping these Space Marines from losing their minds to the suffocating silence.
Bill swept his gaze over the surrounding architecture. The layout of this colony differed entirely from the colossal, solemn gothic monoliths of Terra. Here, the tunnels were defined by stark, geometric steel, reflective metal plating, and exposed conduits of power grids. It looked like the blueprint of an idealized future, yet it now lay tarnished, bleak, and defiled by grease, dried blood, and the warped, cancerous growths of mutants. The entire population of this world seemed to have been corrupted simultaneously by some nameless, catastrophic horror, leaving behind nothing but abominations.
As Bill's squad reached the mouth of the primary transit tunnel, they were greeted by a surging tide of mutants, packed so densely there was no room to breathe. They threw themselves at the Space Marines in a rabid frenzy, driven by beastial instinct to rip the grey-armored giants to shreds. The savage clash erupted instantly.
Bolter fire and chainsword teeth worked in perfect, rhythmic synchronization. Though the Space Marines were heavily outnumbered, they fought as flawless killing machines. The corpses of the abominations began to pile high, yet from the pitch-black depths of the tunnel, the horde continued to pour out without end.
FWOOOOOOSH—BOOM!
The thunderous roar of jet thrusters rattled Bill's chest. He felt the blast of blistering heat and exhaust wash over his shoulder guards as a massive Stormbird gunship descended, hovering right above the swirling dust storm. The gunship dropped to within mere meters of the ground before its heavy steel assault ramp slammed down with a deafening crash.
And from the threshold, a titan stepped forth—or rather, he threw himself into the fray.
The colossal figure in thick, dark-grey armor leaped from the gunship, driving his immense weight directly onto three mutants below. The combination of gravity and mass instantly pulverized the creatures, grinding bone and tissue to mush. The wet pop of their bodies bursting sounded like ripe melons crushed by a sledgehammer. The sheer weight of the massive armor caused the warrior's legs to sink waist-deep into the mountain of fresh carnage.
Bill's eyes widened beneath his helmet. The warrior was clad in a prototype Saturnine Pattern Tactical Dreadnought Armour. It was a bizarre, archaic piece of technology, exceptionally thick and lumbering. Its massive, rounded shoulders and protruding joints made it clear that this suit had not yet undergone the refined engineering of Primarch Vulkan, yet it was the most formidable walking fortress Bill had ever laid eyes upon.
The Saturnine-clad titan moved with slow, crushing deliberate force, like a walking battle tank. He swung his left Power Fist into the skull of a lunging mutant; the energy-shrouded gauntlet vaporized flesh and bone into a fine mist in an instant. Simultaneously, he raised his right arm, which integrated a underslung, multi-barreled Reaper Autocannon, and laid down a heavy barrage into the oncoming swarm.
BANG! BANG! BANG! BANG!
The roar of the autocannon shook the foundations of the tunnel. Exploding heavy rounds tore the mutants in half, cutting them down like wheat before a scythe. Any beast that attempted to breach the wall of lead was instantly crushed into paste by the left Power Fist. The arrival of this iron knight instantly turned the tide back in favor of the 9th Legion. The black talons that had easily torn through the MKII power armor of Bill's squad could not leave even a superficial scratch on the hyper-dense plating of the Saturnine armor.
Shaking off his awe, Bill raised his bolter and provided precise suppressing fire to protect the giant Terminator's flanks. With every pull of the trigger, Bill's twin hearts hammered violently against his ribs. The world before him slowed to a crawl, as if time itself were being stretched.
He could see the sparks spitting from his muzzle, watch the micro-rocket bolts pierce the chest cavities of the abominations before detonating within to spray viscera, and smell the metallic tang of fresh blood leaking through his helmet filters. The seductive, sickening sweetness of the blood-scent triggered the Red Thirst within him. His throat burned, and his jaw clenched shut. Bill had to exert an immense effort of will to suppress the beast within while his fingers remained resolute on the trigger.
They pushed further into the dark, stagnant tunnels. The unending thunder of gunfire strobed against the concrete walls. The tearing screech of chainswords and the shrieks of the dying created a deafening resonance; had any Astartes been without his helmet, the sheer pressure of the noise in this enclosed space would have shattered his eardrums.
The Saturnine Terminator remained the tip of the spear. Even after his autocannon ran dry of ammunition, he used his massive bulk and Power Fist to hammer his way forward, leaving thousands of shallow claw marks etched into his thick, scarred plating.
But amidst the chaotic smoke and dust, a mutant of unnatural speed and agility climbed over the heads of its kin. It launched itself off the dome of the Saturnine Terminator's hood, leaping through the air with its maw wide, revealing long, black fangs and razor claws. Its target was the Space Marine providing fire support from the rear.
Its target was Bill.
CRASH!
Caught off guard, Bill took the full impact of the beast in his chest, sending him crashing onto the wet pile of corpses. His bolter slipped from his grasp, lost in the shadows. Pinned to the ground by the creature's immense weight and strength, Bill reached frantically for the chainsword and chainaxe at his waist, but his fingers clawed only empty air.
Beneath his visor, Bill's eyes stretched wide in alarm. He gathered his strength and repeatedly drove his armored fists into the creature's grotesque face, hoping to throw it off. Yet, the mutant did not budge. It possessed physical strength that rivaled—or even surpassed—his own augmented biology.
Unhinging its jaw, dripping with thick, dark saliva, it lunged down to tear Bill's head from his shoulders. Bill twisted his head violently at the absolute last second. Death missed him by a fraction of a millimeter as the beast's jaws clamped down hard onto his left pauldron instead.
CRACK!
The abomination's fangs and claws were incredibly strong, tearing through the heavy ceramite plating as if it were parchment. Crimson warning runes flashed across Bill's HUD, signaling critical structural failure in his left shoulder. The beast thrashed its head in a rabid frenzy, ripping the pauldron completely off his armor.
Before it could lean down to tear into his exposed neck, three bolter rounds detonated at point-blank range.
BANG! BANG! BANG!
The mutant's head vaporized into a shower of gore, and its lifeless carcass collapsed heavily onto Bill. Standing over him, smoke still curling from the muzzle of his bolter, was Rapha. He had saved Bill's life in the nick of time.
Bill shoved the carcass aside and dragged himself up with great difficulty. He stared at his left shoulder, where exposed cabling hissed beneath the shredded remains of his armor.
Rapha stepped closer, bending down to retrieve a fallen chainsword from a deceased legionary, and handed it to Bill.
"Stay sharp, Grayson," Rapha's flat voice crackled over the vox. "I have no desire to see you lying next to Ricario and Caius just yet."
With that, Rapha spun back and unleashed a fresh volley of fire into the oncoming horde.
"My thanks, Rapha." Bill gripped the hilt of the chainsword tightly, purging the lingering dread from his mind. He revved the weapon, its teeth spinning at maximum speed with a high-pitched scream. Bill surged forward from the rear guard, plunging directly into the bloody melee alongside his brothers, whose grey armor was already dyed a hellish crimson by mutant blood.
Bill's blade swept through, cleaving the first mutant in two, followed by a second, a third, and a fourth with terrifying, brute strength.
Yet, amidst the harrowing slaughter, a sickening sight began to unfold. Some of the 9th Legion Astartes were losing their grip under the pressure of the Red Thirst. They abandoned all sanity, discarding their empty weapons to charge the horde bare-handed. They bared their teeth, trying to tear and consume the raw flesh of their enemies, only to be overwhelmed by the sheer mass of the mutant tide and torn to pieces in the dark.
It was a scene far more monstrous and horrifying than any combat Bill had experienced against the Thunder Warriors on Terra. At least those thunder-born giants, though unstable, fought with martial honor. But the enemies and his own maddened brothers in this tunnel... they had become twisted, hideous, and entirely devoid of a soul.
Even so, the underworld nightmare of Neptune ground on, and Bill had no choice but to keep swinging his blade in this dark, endless hell.