Riku Sakamaki, a high school student, wakes up in a world where the sky glows purple. He has been transported to this strange place with no idea how or why. The first person he meets is a silver-haired girl named Vestia Zeta, an agent of a secret organization with the codename V.7. She wears key-shaped accessories and has access to data from the virtual world. Cool and mysterious on the outside, she also has a sarcastic, sometimes clumsy side that makes her oddly charming.
"[cold]You'll die her
Vestia Zeta: Heir of the Black Key - At the End of Resonance — The Tomorrow Unlocked by the Key
In the northeastern part of Lumina Centra, there was a place called the Disposal Sector. Buildings that had once been crystal ore refining factories stood in rows, now uninhabited. Broken windowpanes rattled in the wind, and the crystal lamps along the walls had long since gone dark. Beyond the ruins, a thirty-meter-tall frequency tower cast a black shadow.
That tower seemed darker than usual.
"Almost there."
The silver-haired girl spoke in a low voice. Her waist-length hair was loosely tied back, and her bluish-silver eyes stared straight into the depths of the ruins. The white key pendant at her neck carried a faint white glow.
"You're still not at full strength. You really planning to let me go in alone?"
The black-haired boy spoke while staring at the back of his right hand. There, the black key's crest flickered faintly, as if breathing. How many days had it been since the transfer? He'd grown so accustomed to this world's dark sky that counting had become a chore.
"It's not that I can't fight. Besides, if I don't go, you'll just go berserk on your own again."
"I won't go berserk. ...Probably."
Vestia stared at Riku's face, and the corner of her mouth curved just slightly. It was an expression that could have been either a smile or exasperation.
The two had come here because of a message from the information broker, Kisaragi Ren. In the back of the old town's information café Signal, Ren had dropped his usual elusive smile and said: *"A jamming device's signal was detected in the northeastern Disposal Sector. Most likely the work of that song person."*
A device that stops the frequency towers' purification waves. If something like that activated, Lumina Centra's safe zone would vanish in an instant.
"Your face still looks pale."
Riku stole a glance at Vestia's profile as she walked beside him. It had only been a few days since she'd gotten up from the bed in the medical sector. The wound in her abdomen was closing, but far from healed. Riku knew that with every step she took, her breathing grew slightly ragged.
"Shut up. If you're going to worry, say something more useful."
"It'll be fine. We'll manage."
"That's your usual catchphrase. Nothing's been managed so far."
"We'll manage."
After that brief exchange, the two walked in silence through the ruins. Glass shards underfoot crunched beneath their shoes. A world without sound. Even the wind seemed to be blowing somewhere far away.
Then, the air changed.
Heavy. As if they'd wandered into the belly of some enormous creature, the space itself pressed down on them.
The back of Riku's right hand grew hot, tingling.
"He's here."
At the entrance to the ruins, in front of a crumbling factory building, a man stood. Tall, with long silver-blue hair tied back in a single tail, flowing in the wind. His left eye was covered by a mechanical monocle, his right eye crimson. Just by standing there, he drained the sound from the surrounding air.
"Well now, I've been waiting. Heir of the Black Key. And the girl of the White Key."
Decibel's voice resonated as if seeping directly into their ears. The air trembled, and sound rippled like waves beneath their feet.
"Decibel..."
Riku's teeth chattered faintly.
"Glad to see you're well. Have you lost weight? Ah, yes—Vestia Zeta, is your wound all right now? The pain from that time is not something my song can heal."
Vestia's silver eyes narrowed sharply.
"I have no reason to be worried about by you."
"Is that so. Very well. But today, I thought I'd gift the two of you a special concert. I'll turn every citizen of Lumina Centra into an orchestra and play the finest melody of unease."
Decibel raised his right hand. Something glinted at his fingertips. A tuning fork. Two slender pieces of metal built into his fingers.
He flicked his fingers.
*Crack.* The air split.
Sound became a wave, shaking the surrounding ruins. Then, deep in Riku's ears, a high, sharp tone raced through.
In that instant, the lights of Lumina Centra went out, one by one.
The frequency towers lined along the western outer wall. The purification wave lights spinning at their peaks dimmed, one after another. All five towers fell silent at once, quietly.
"Wha... what did you—"
Screams could be heard from the distance.
The safe zone was gone. A swarm of Noise came flooding in from beyond the boundary, toward the city.
"Listen well. This is merely the prelude—to play the instrument that is your fear."
Decibel smiled. Only his mouth drew a thin arc as his crimson right eye glared at Riku.
"Don't screw with us...!"
Riku tried to charge forward. The black key's crest flickered on the back of his hand.
But before he could, Vestia's hand grabbed his left wrist.
"I'll take the front line. You stay back and focus on controlling the black key."
"Do you even hear yourself? Your wound's still—"
"That's exactly why. I'll be your shield. You watch the whole field."
Her fingers dug into Riku's wrist, hard enough to hurt. But that hand was trembling faintly. Riku felt it.
"No. I'm taking the front. You fall back and support."
"Don't say stupid things."
"You're the stupid one. Just get back. I'll stop him first."
Riku shook off Vestia's hand. His tone was clearer than even he expected.
Vestia's eyes widened for a moment.
"Don't push yourself. Promise me."
"It'll be fine. We'll manage."
Riku stepped forward with his right foot. Black particles began to dance above the cracked concrete of the Disposal Sector. Decibel's song, urging the birth of Noise, crawled low, low through the air.
"Magnificent. Truly magnificent. Carrying fear, yet still standing against me. Like a flightless little bird flapping toward a storm."
Decibel's fingers struck the tuning fork again.
High and low tones rang out simultaneously. The two sounds collided, warping the air. Behind him, black haze began to swirl. The haze drank in the screams, expanding as if breathing.
"Four hundred fifty thousand people of Lumina Centra are now in terror. That terror is the finest nourishment for Noise. Behold—the monster born from the city you tried to protect."
The black haze suddenly stretched upward.
Twenty meters tall. No—still growing. Easily surpassing the abandoned buildings, swallowing the surrounding structures, a colossal Noise took shape.
Where eyes would be, countless red dots floated.
"No way..."
Riku's voice trembled.
The colossal Noise's tentacle slowly rose. Several meters thick. Dripping black mucus, it swung down carelessly.
An abandoned building shattered to pieces.
Steel frames bent and twisted, concrete burst apart. The roar arrived a beat later. The ground shook. Rubble at Riku and Vestia's feet bounced and clattered.
"Riku, get back!"
Vestia stepped forward. The white key pendant blazed with light. White patterns floated around her, and a barrier of light spread outward.
The colossal Noise's tentacle slammed into that barrier. A violent vibration. Vestia's face twisted in pain.
"Vestia!"
"I can't afford to fall yet. You—ready the black key. My barrier won't hold more than a few more hits."
Riku looked at his right hand.
The black crest burned like fire.
*(Am I going to lose control again?)*
His heart pounded with an ugly rhythm. Memories surged from the back of his mind. The underground passage collapsing. Vestia fallen, bleeding. People getting hurt because of him. The world breaking because of his power.
*(Even so—)*
Riku clenched his teeth.
He had decided to step forward.
"Please, black key... just this once, listen to me!"
Riku thrust out his right arm. The black crest sent black light racing from his fingertips to his wrist. Like ink soaking into skin, the black key's crest fully surfaced.
A black wave shot forward.
The moment the colossal Noise's tentacle touched the black light, it vanished without a trace. The black haze scattered, and a massive hole opened in the Noise's body.
"It worked...!"
But the next instant, Decibel began to sing.
His voice traveled through the air, flowing directly into Riku's ears. Not words. A song of pure sound. An unpleasant vibration that stirred the depths of his brain.
Riku's vision warped and twisted.
The fire from his childhood. The burning house. The city reduced to rubble. Screaming voices. Wanting to help, but his body wouldn't move.
The rampage right after the transfer. Black light overflowing from his hands, tearing open empty space. He was terrified. He didn't know what he had destroyed.
And the night Vestia collapsed, bleeding. The darkness of the underground passage. Red spilling from her abdomen.
Three memories slammed into Riku's mind simultaneously.
"Aaaaaaahhh!!"
Riku clutched his head and screamed.
The black key's light went wild. From Riku's right hand, uncontrolled black waves radiated outward. A nearby abandoned building was blown to pieces. The ground split.
"Ah, beautiful. The black key within you responds to your fear, trying to devour you along with it. That suffering becomes sound, reaching even me."
Decibel's song grew stronger. Deep in Riku's ears, screams, the sounds of fire, and the smell of blood mingled together.
"Stop... just stop...!"
"Very well. I'll stop. In exchange, use that power of yours to erase the silver-haired girl before you."
The black key's rampage began to turn toward Vestia.
In that instant, Riku felt something soft against his back.
"...You idiot. You said you'd protect me."
Vestia was embracing him from behind.
Her white key pendant pressed firmly against the back of Riku's right hand.
White light touched the black crest.
Something flowed into Riku's body. He couldn't tell if it was cold or warm. But deep in his scrambled mind, a quiet sound resonated.
The black waves were enveloped in white light. The rampaging energy of the black key transformed into soft white ripples, slowly spreading outward.
The insects of memory that had been so loud suddenly fell silent.
"I'm right here. So don't carry it all alone."
Vestia's whisper reached Riku's ear, close enough to feel her breath.
"Wh-what the... don't just suddenly hug me..."
Riku couldn't keep his voice from cracking. His heart was pounding for a completely different reason now.
"I had no choice. This is the most reliable way to stop an idiot who's about to go berserk."
Vestia's arms tightened around him.
"Your body... your wound's still—"
"I'm enduring it. So hurry up and finish this."
On the back of Riku's right hand, the black key and white key glowed simultaneously.
Black light and white light mixed, swirled, and became a single, quiet ripple. The ripple spread toward the colossal Noise—slowly, but surely.
Wherever the light touched, the Noise dissolved away.
The twenty-meter-tall black body scattered into particles without a sound, dispersing into the sky. Tentacles, red dots—nothing remained. It was completely purified, not even leaving a Noise core behind.
"Impossible... impossible!!"
Decibel raised his voice for the first time. The monocle over his left eye flashed red.
"The black key and white key, resonating? That's nothing but a fairy tale from legend."
"Can't you see it? If what's happening before your eyes is your delusion, why don't you go cool your head?"
Vestia's usual sharp tongue had returned.
Decibel stepped back.
"...But this is not the end. Your harmony is far too fragile. Someday, dissonance will surely tear that bond apart."
Decibel operated something.
Deep in the Disposal Sector, the jamming device let out a loud noise.
"Damn it—he's raising the jamming device to the brink of detonation. If that explodes, the frequency tower shutdown becomes permanent!"
Vestia tried to pull away from Riku.
"Wait here. I'll—"
"No. I'll do it."
Riku gripped the black key's light. After resonating with the white key, the black key was strangely quiet, resting calmly in his hand.
Riku sprinted toward Decibel.
"As if you could touch me."
Decibel struck the tuning fork. Blades of sound tore t
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