Fate's Slave - Shadow Slave X Honkai Star Rail

”W—What was that noise?”

Huohuo’s voice quivered in response to the dark destrier’s cry. Sunny paid her no heed, since the question wasn’t directed towards him. Instead, he walked deeper into the darkness of the mansion.

Besides him, a tenebrous steed with adamantine horns and wolf-like teeth snorted. Nightmare’s haunting crimson eyes flared as his hooves clicked against the wooden floorboards. Augmented by two of Sunny’s shadows, the Ascended Terror’s might soared far beyond what would normally be possible. In the next moment, Nightmare dived into the world of shadows, galloping off.

Back when Sunny first met Phantylia’s true Heliobus form after killing Tingyun, he had attempted to strike her intangible body with Hail Sorrow. The black blade was not only capable of dealing damage to the mind, but thanks to Sunny’s natural affinity, was able to strike shadows as well, destroying the soul.

Neither function had worked on Phantylia. Heliobi were naturally immune to soul attacks — they didn’t even cast shadows in the first place — and Hail Sorrow’s mind attack required physical contact in order to take root. Thus, he had been completely unsuccessful back then...

Due to that failure, he had immediately assumed that Heliobi couldn’t be harmed by mental afflictions.

In reality, they could. The mind attack only needed to be direct, not requiring conditions such as ’needing to physically wound’.

That was why he summoned Nightmare. The Shadow Creature’s entire repertoire of insidious powers took the form of mind attacks. [Mantle of Fear] to inflict a sense of supernatural horror upon his prey. [Nightmare] to plant a seed of terror into their hearts, before harvesting it in order to gain more power. Finally...

There was the [Dream Curse].

Tearing his gaze away from the darkness, he found an object left on the ground. Tilting his head, he picked up Sushang’s flashlight, which was haphazardly dropped on the ground like the wrapper of a lollipop. He had an unimpressed look when he looked up.

Sushang was clinging onto Guinaifen like a koala — whatever a koala was supposed to be — staring with a gaping jaw where Nightmare had been a few moments earlier. As for the explosive streamer herself, she seemed to be having a hard time trying to push her companion off, considering how both of her hands were occupied with her phone stick and staff.

Unlike before, however, her bright and sociable personality momentarily disappeared, a sharp kind of caution in her gaze, which swept between Sunny and the darkness behind him.

That was to be expected of a Legacy. Their ’culture’ was to ingrain as many killer instincts into the minds of impressionable children as they can, giving them a proper advantage in the cruel world of the Nightmare Spell and Paths.

It seemed to work, at the very least.

Huohuo was still quivering in fear with covered eyes, with Tail peeking out from behind her.

Summoning the Covetous Coffer, Sunny reached in and pulled out a cold can of soda. There was some pretty bird lady on it as an advertisement stunt. He sat against the wall of the corridor.

Pulling on the tab, there was a click followed by a sizzling sound.

”Now... we wait.”

He ignored the way the building violently shook.

***

...Nightmare’s form solidified once more, coalescing out of liquid shadow. Crouching down, the black steed rested upon the mansion’s floor, bearing its serrated teeth in animosity.

A moment later, something imperceptible flowed into the world.

It seeped into the walls, soaked into the floors, coated the ceiling. It shrouded anything and everything, rushing through the labyrinth of corridors.

Nightmare sang a silent lullaby, and as payment...

The haunted house fought back.

In a quick move, Nightmare got back onto his four legs, rushing forward. The floor below his previous position splintered, the jagged edges of wood sharply tearing upwards as if trying to pierce him.

The walls next to the tenebrous steed suddenly tore open, revealing a terrible maw formed out of rotted wood. The shattered wall curled into a smile, before bending inwards as it attempted to gnaw on Nightmare’s flesh. However, Nightmare was simply too quick, too swift. By the time the two broken ends of the wall clamped down, he was already galloping into the next corridor.

Suddenly, the wall peeled open, revealing a window that had been purposefully boarded off. That window shattered... but the glass that did not fall. Instead, it hovered in the air for a moment, before rotating so that the sharp edges were pointed at Nightmare. Then, with all the rapid fire of a machine gun, the glass blasted towards him at disastrous speeds.

Of course, Nightmare was faster.

The sound barrier was repeatedly shattered as the glass fired off from its floating position, each shard trailing behind Nightmare like the promise of a death from a thousand cuts. Rather than piercing his black hide, however, they ended up embedded into the walls and floor as Nightmare swiftly dashed past.

A sharp crack resounded as the walls broke apart, separating into dozens of wooden stakes that seemed to zigzag as they tried to impale Nightmare. Making plenty of sharp turns, he escaped their assault.

The mansion continued to assault Nightmare, each attack growing more vicious, more relentless... more desperate. There was a reason for that — and it was not simply because the Heliobus was growing frustrated, though, that was true.

There was a reason why it had only just began to attack, and why it specifically targeted Nightmare. It was simple, actually.

Sunny summoned the Terror not due to the [Mantle of Fear], nor the [Nightmare] Ability — it was relevant, however.

Rather, he summoned Nightmare for his Terror Ability... [Dream Curse].

The Heliobus was currently under the assault of Nightmare’s horrific lullaby. Whether Heliobi were able to sleep wasn’t something Sunny or his steed knew, but that didn’t matter.

Because at this moment, the Heliobus was panicked precisely because the lullaby was taking effect.

By Nightmare’s authority, the Heliobus will eventually fall into his labyrinth of nightmares, and succumb to his thousand hells.