Fate's Slave - Shadow Slave X Honkai Star Rail

The Underworld was quieter than it had any right to be, though not truly silent.

The distant groan of machinery echoed through the industrial labyrinth, uneven and strained, like a failing heartbeat struggling to maintain rhythm. Dim lights flickered overhead, casting long, distorted shadows across rusted metal structures and fractured stone pathways. The entire place felt tense, as if something unseen was pressing down on it, waiting for the moment to break through.

At the center of that suffocating stillness stood a Nightmare Gate.

It had not yet opened, but its presence alone was enough to distort the space around it. The surface of the Gate pulsed faintly, like a wound that refused to close, its edges trembling as though something on the other side was testing the barrier. The air around it felt wrong — heavy, warped, carrying a pressure that dug into the mind more than the body.

A soft whistle broke the tension.

Aventurine stood a short distance away, his posture relaxed in a way that felt almost insulting given the situation. One hand rested casually at his side while the other remained tucked behind his back, his polished armor gleaming faintly under the dim light. The mask-like helmet obscured his face entirely, reflecting nothing, yet the slight tilt of his head suggested amusement rather than concern.

"Well, isn’t that interesting?"

Beside him stood a woman who seemed almost too refined for the Underworld’s harsh environment. Her silver hair fell neatly around her shoulders, framing a composed and sharp-featured face. She wore a fitted uniform of black and red with gold accents, a design that balanced elegance and practicality with unsettling precision. A long coat draped behind her, shifting slightly as she adjusted her stance, its inner lining catching the faint light.

At her feet, a small creature shifted.

The Warp Trotter was compact and round, its dark body contrasted by gold accents that gave it an almost ornamental appearance. Its ears twitched as it surveyed the area, though its expression — or what passed for one — seemed largely unimpressed by the looming threat of the Gate.

The woman crossed her arms, her gaze fixed on the pulsing anomaly as her expression tightened slightly.

"So, are the odds looking bad even for you, Aventurine?"

Aventurine let out a quiet chuckle, the sound carrying an easy, almost playful confidence.

"The odds are always stacked against me. I just happen to come out on top."

He studied the Gate for another moment before shaking his head faintly, as if mildly disappointed.

"Another Nightmare Gate opening directly beneath the one above. That abomination of Fate really isn’t making things easy. I’d give it about four minutes before it opens."

Topaz glanced at her phone, her lips curling into a faintly smug smile.

"Four minutes? Unlike you, I actually bothered to invest in some Spelltech. It’s closer to three."

Aventurine sighed dramatically, though there was no real frustration behind it.

"Geez, don’t get on me just because the strong don’t need such pitiful things. Besides, you’re wrong. It’s going to open a little later than expected."

Topaz’s expression flattened immediately.

"And why is that?"

Aventurine shrugged.

"Just a hunch."

She stared at him for a moment, unimpressed, before letting out a quiet exhale.

"Of course."

The Gate pulsed again, this time with more force, as if reacting to something unseen. Aventurine tilted his head upward slightly, as though he could perceive what was happening above them, beyond layers of stone and distance.

"I was supposed to return to dealing with that Corrupted Saint, but it looks like we’re about to have a bigger problem."

From within his coat, he retrieved a small device etched with faintly glowing runes. Pressing a button, he raised it slightly as his voice carried through the connection.

"Miss Clara, I’d advise you to begin evacuation procedures in the Underworld as well. We have another Category 4 Gate forming."

Topaz’s composure broke instantly. She snapped, turning toward him in disbelief.

"What?! But this one only has a four percent chance—"

Aventurine’s grin widened beneath his mask, evident only in the slight lift of his posture and tone.

"There are those who are Blessed by Fate and those who are Cursed by it, but it’s rare to encounter someone who is both."

He turned his attention fully back to the Gate.

"This looks like misfortune, but in reality, it’s an opportunity. When it comes to luck, it’s not about what you’re given — it’s about how you use it."

White sparks gathered in his palm, coalescing into a small, unassuming stone orb. Despite its simplicity, the space around it distorted faintly, as though reality itself resisted its presence.

Topaz narrowed her eyes.

"A storage Memory?"

"Something like that."

Before she could question him further, the orb pulsed. In an instant, both she and the Warp Trotter were reduced to streaks of light and drawn into its surface, disappearing completely.

Aventurine closed his hand around the orb and glanced once more at the Nightmare Gate. Then, tilting his head upward, he spoke quietly.

"Let’s see how this plays out."

At his command, his armor responded instantly. Light flared beneath him as he launched upward, the ground cracking under the force as he accelerated at impossible speed through the vertical expanse of the Underworld.

As he rose, a strip of cloth appeared in his hand. Without hesitation, he wrapped it over the eyepieces of his helmet, covering them completely.

Blindfolded, he continued ascending without the slightest hint of hesitation.

Below, in the shadows of a narrow alleyway, something shifted.

Veliona stepped forward, her crimson eyes glinting with interest as she watched the direction Aventurine had gone.

Her gaze drifted toward the Nightmare Gate, lingering for a moment as if measuring something unseen. Then she closed her eyes, and her form vanished as though she had never been there.

***

Above, the battlefield had long since returned to chaos.

Sunny moved through it like a living weapon, his presence turning the tide with overwhelming force. Hail Sorrow cleaved through another of the black-scaled lizards, the blade passing so cleanly that the creature split in half before it could even react. Before its body hit the ground, Sunny was already moving again, his hand plunging into the hollow eye socket of another creature and tearing free something vital. The Nightmare Creature convulsed violently before collapsing lifelessly at his feet.

He did not slow.

The shadows themselves had become extensions of his will, reacting instantly to his intent. Spikes erupted from the ground, impaling creatures mid-charge, while elongated tendrils pierced through multiple enemies at once. Rotating constructs of darkness carved through clusters of Nightmare Creatures, reducing them to shredded remains in seconds.

When one lunged at him from the side, he didn’t even look at it. Instead, he shifted his blade slightly and cut through its shadow. The effect was immediate. The creature froze mid-motion before collapsing, its soul severed directly.

At the edge of his perception, he could feel Saint.

The battle beyond the walls was escalating, each clash sending tremors through the ground. But what concerned him wasn’t the intensity — it was the trajectory. Saint was losing ground, not in a sudden or catastrophic way, but steadily, inevitably.

Cocolia was too strong.

Too adaptive.

Too aware.

Sunny’s grip tightened slightly.

Then something new emerged.

He felt it before he saw it.

When his gaze snapped toward the Gate, the difference was immediately apparent. The creature that stepped through resembled the others in shape, but its presence was entirely different. It was larger, its wings spanning wide, but what truly set it apart was the dark mist seeping from its hollow sockets.

The shadows recoiled from it.

Where the mist touched, they vanished entirely.

Sunny’s eyes narrowed.

This was not shadow. It was not simply the absence of light.

It was something else entirely.

True Darkness.

Sunny raised his hand.

Flame ignited instantly, burning bright and pure. The moment it appeared, the mist recoiled, driven back by the light. At the same time, the surrounding shadows surged forward, strengthened by the presence of that light as they pierced into the creature’s body from multiple angles.

Sunny paused only briefly before Tingyun’s voice echoed in his mind, calm and reassuring.

[It’s alright, Benefactor.]

He nodded slightly.

The flame shifted, condensing and reshaping until it formed a second blade in his hand, its edge blazing with intense heat. Unlike Tingyun who was at the Dormant Rank, Sunny was able to create flames of the Ascended Rank. Furthermore, he was even able to manipulate its shape.

After long contemplation, he deemed to name his ability to use a Shadow’s Abilities by summoning them in his Soul Sea: Shadow Extension.

Without hesitation, he moved.

Now wielding both shadow and fire, he tore into the Awakened Devils pouring from the Gate. Their scales offered little resistance, cracking under the combined assault. Some attempted to ignore him, slipping past his influence, but they were quickly intercepted by the Awakened soldiers, who had regained their footing under Bronya’s enhancement. 𝗳𝚛𝗲𝕖𝚠𝚎𝚋𝗻𝗼𝕧𝗲𝐥.𝚌𝚘𝐦

Still, something felt off.

Sunny noticed it quickly.

They weren’t thinking.

For creatures of their rank, that was wrong. Devils were supposed to be intelligent, capable of strategy and coordination. Instead, they fought like Beasts, driven purely by instinct and frenzy.

His eyes flickered as realization set in.

Tingyun’s flames weren’t just destructive. They stoked the heart. By stoking a Nightmare Creature’s desire to consume the souls of humans, any notion of intelligence they once had disappears.

Sunny allowed himself a faint grin.

Moments later, a larger figure emerged.

An Awakened Tyrant.

Its presence was overwhelming, waves of True Darkness pouring from its body as it roared. But despite its power, its movements were unrefined, its attacks wild.

Sunny stepped forward, ducking beneath its swing with ease. In one smooth motion, his blade flashed, severing its head cleanly as darkness spilled from the wound instead of blood.

He turned immediately, ready to strike again—

Only to find the next Devil already gone.

Pulverized.

Sunny blinked, momentarily caught off guard.

"Hey there!"

The voice was casual, almost cheerful.

Sunny turned slowly.

Aventurine stood there, one hand raised in greeting, the blindfold still wrapped over his helmet.

He looked entirely at ease, as if he had just walked into a casual conversation rather than the middle of a battlefield filled with monsters.

Sunny stared at him for a moment before speaking.

"Why the hell are you so flashy?!"

Aventurine grinned:

"Fashionable, you mean."