Resonance: Threshold

[November 17th, 09:00 JST]

Tokyo Prefecture – Harmonia Foundation Tama Facility, Virtual Sim Room Alpha-01

The lift chimed with a soft ding as its doors slid open.

The vast hollow of the simulation room stretched out before them. The underground chamber spanned wider than two soccer fields. Its polished black floor was segmented by faint geometric lines that connected to sigil markings spread across the surface. The patterns blinked in slow intervals, as if the room itself had noticed a Diva’s presence.

An enclosed observation deck lay not far from the entrances, overlooking everything in the chamber like a command bridge.

Reina signaled for the rest of Tempesta Unit to remain in the chamber. She and the recruits stepped onto a smaller side platform that rose toward the deck. Takeshi stood behind her wheelchair, guiding it as the platform ascended.

Once inside the observation deck, he rolled her to the front window before turning to the control console. His hands moved with practiced precision as he brought the system online.

The recruits lined up behind them in nervous silence, their eyes wide as they took in the sheer scale of the room.

Below, the six girls of Tempesta Unit stood in a circle at the center of the chamber, white coats stark against the dark floor.

Above them, a medium-size meteorite fragment hung in midair, held by a framework of reinforced pillars — one of the rare Novium stones excavated from the ancient lost ruin. The surface carried looping runes and music-like notes that pulsed in sync with the sigils around the room.

When a Diva sang inside Alpha-01 and her resonance passed through the chamber, the stone responded. The stored frequencies within it would be awakened, projecting CODA constructs based on the ancient recording etched into it. Illusions in form, but as lethal as the real thing if unprepared.

Because of that, one detail on the control panel in front of Takeshi stood out more than anything else: a large red emergency switch. A single press would force a reverse frequency through the chamber, instantly cancelling every resonance, shutting down the meteorite and anything it had summoned.

Reina glanced over the rows of recruits behind her.

“I’m sure most of you already read the orientation booklet you received last night. But in case you haven’t, let me explain again.”

She raised her voice just enough for the entire deck to hear.

“Diva awaken from two major magical trees. Can someone tell me what they are?”

A recruit lifted her hand nervously.

“Y-Yes. Elemental Cantus… and Conceptual Cantus…”

“Correct.” Reina nodded. “The first one covers the natural elements: fire, water, wind, earth, and lightning. The things you see every day. In my case, I’m a Lightning-type Diva.”

She took out her D-Mic and hummed softly into it, a small spark of electricity flickered around her before fading away.

“The latter manipulates forces that don’t exist physically: gravity, light, and more waiting to be discovered. My team will show you what I mean.”

She turned to Takeshi and gave a small nod.

Takeshi leaned forward to the microphone.

“Alright, girls. Button up your coats. The simulation is starting.”

He flipped a switch as he spoke.

The chamber below replied with a quiet whir that deepened as the system warmed.

In the center, Emi and the others closed their formation, each lifting her D-Mic. Their voices rose together, their song wordless yet synchronized.

Above them, the suspended Novium stone flickered. Its runes lit unevenly as they responded to their resonance.

At the far end of the field, a mass of mist thickened. It was slow at first, then crawled inward until it clumped into a dark cloud with glowing eyes inside.

A mixed horde of Level 1 and Level 2 CODA took shape.

“They’re here!” Emi called out. Her voice rang clear across the chamber.

“Battle formation! On me!”

Emi stepped forward. One by one, the girls invoked their Cantus. Runes lit up in their eyes as musical-note sigils traced upward along their bodies, wrapping them like shifting tattoos of light.

“Ars Aria: Aqua Cantus.”

“Ars Aria: Ignis Cantus.”

“Ars Aria: Terra Cantus.”

“Ars Aria: Ventus Cantus.”

“Ars Aria: Gravitas Cantus.”

“Ars Aria: Lux Cantus.”

Sigils of multiple colors lit up across the chamber in response to their Ars Aria. Misaki raised her hand toward the center of the horde; the black sigil opened and a dense gravity sphere materialized, pulling nearby CODA toward it. Several of them thrashed, trying to break free from its pull.

Mika and Emiko moved together in perfect beat. Walls of compressed earth rose around the struggling horde, their surfaces wrapped in a thin layer of light that reinforced the structure. The barrier tightened, its glow bracing the walls against the impact of the trapped CODA.

Nana stepped in next. With each punch she threw, bursts of fire shot out from her surrounding red sigil and slammed into the enclosed space. Heat built rapidly inside the chamber, and the horde within began to burn under Nana’s raging flame.

Momoko and Emi handled the stragglers. Whenever a CODA slipped free of range, their wind and water intertwined to drag it back toward the center. Each stray was tossed upward, caught in Misaki’s gravity sphere, and dropped straight into the blazing enclosure below.

It didn’t take long.

On the observation deck, the monitor flickered before displaying a simple message:

CODA neutralized. Ending current simulation.

“Great job, girls. Take a short rest. That was a beautiful combo you pulled off,” Takeshi said through the microphone.

Reina looked back at the recruits. Their eyes sparkled with excitement; awe was written plainly across their faces. She used their enthusiasm to move on to the last part of today’s class.

“Now that you have seen how an Ars Aria works and what its magic looks like, let us continue. Next question. How many grades of Diva are there?”

“Four,” the recruits answered together.

“Correct.” Reina nodded with a small smile. “All of you have just resonated with your D-Mic, so you are currently at the Fundamental Aria Grade. When you become more in tune with your resonance and are able to invoke a Cantus that belongs to one of the families, you will reach the Advanced Aria Grade. This is the minimum requirement for performing on stage.”

A few recruits exchanged glances and whispered among themselves. Their earlier excitement had shifted into genuine interest.

Reina looked down at her team resting in the chamber below.

“My team is at the Cantus Level Grade. This is the requirement for real combat. A Diva must reach this grade if she intends to fight CODA. There are no exceptions.”

She paused. “… Emi?” Reina searched for her among the group, but Emi was not with the others.

“The next grade is the Cantus Major Grade,” a gentle voice said behind her. “And that is the one Reina-chan holds. She is one of the very few Divas in the Foundation with this grade.”

Reina didn’t need to turn to know who it was. Emi stepped closer and wrapped her in a small hug. Reina turned her wheelchair slightly and returned her smile.

Takeshi watched the two of them with a quiet smile before addressing the recruits. 

“There is one more grade. It exists in theory, but we have no record of anyone reaching it. The ancient murals mention it only briefly. The final stage is called the Symphony Major Grade. It is said that if a Diva ever reaches this state, her Ars Aria could rewrite the very laws of the world. Something close to a divine power.”

The recruits reacted instantly.

Some stiffened.

Some leaned in.

One covered her mouth with disbelief.

Another whispered, “Rewrite the world…?”

Reina nodded slowly. “Don’t think too much about it. In the end, it is only a theory. Knowing it exists is enough.”

She turned her gaze back to Emi. “So, what brought you up here?”

Emi smiled sheepishly. “Nana-chan asked if you could raise the difficulty to Level 3 CODA. She said she wanted to try fighting it together.”

“But you cannot fight level 3 without a Cantus Veil,” Reina replied.

“Actually, we can.”

Takeshi smiled, and every eye turned toward him.

“I was asked to test a prototype system today. It mimics your Cantus Veil, Reina. The effect is almost the same, though weaker. If it works, it means future Aria Corps units can have a Veil without needing a Cantus Major-Grade Diva in the team.”

Reina sighed, “Sure, go ahead.” She paused for a moment. “Good luck, help me relay it to the others.”

“I will!” Emi replied, and she hurried back toward the small platform.

Reina watched as Emi rejoined the team below.

“Will Level 3s put too much pressure on them?” Reina asked quietly. A hint of worry slipped into her voice.

“They need to learn how to handle them sooner or later.” Takeshi answered. He lifted the microphone and spoke into it.

“Girls, your request is approved. Level 3 cluster incoming.”

He flipped another switch.

The runes on the meteorite began to blink faster, the sigils responding to the higher threat level they were about to generate.

Five elephant-shaped CODA emerged from the mist generated by the meteorite. Their bodies were massive, the same oversized scale as the Level 3 lion Reina had fought before.

A moment later, the entire chamber was wrapped by the artificial Cantus Veil. It could not be seen, but the six girls in the room felt it instantly. Charged mana drifted through the air, almost identical to the sensation when Reina invoked her own Veil.

As the girls raised the D-Mics and began chanting their Ars Aria, the Level 3 CODA charged. Sigils appeared across the arena floor.

Then something went wrong.

The CODA flickered violently. Red warning lights flashed across the control deck. Takeshi’s hands flew across the panel.

“What happened?” Reina asked.

The Level 3 constructs froze mid-charge.

The recruits behind her stared with wide, terrified eyes.

Emi and the others stood ready in the chamber below, confused but bracing for anything.

“The resonance is going out of control,” Takeshi said with panic in his voice. He slammed his palm onto the red emergency switch. Nothing happened. “No response… damn it!”

He tore open a secondary keypad and typed furiously, trying to override the system.

Below, the Level 3 CODA began to melt, yet mist was never supposed to melt. Emi and the others sensed danger immediately and stepped back.

The liquefied mass started to reform.

Above them, the meteorite pulsed with blinding light. The runes flashed at impossible speed, like someone flickering a flashlight on and off faster than a human hand could move.

The fused mass reshaped into a towering snail-like creature. Its shell twisted open, revealing rows of blinking eyes.

Its roar shook the chamber. Even the observation deck trembled.

“Level… four…” Reina whispered, unsure how to react.

Takeshi was still typing, desperately trying to regain control. Reina wanted to run, but her legs refused to respond.

I cannot let them be in danger!

She gripped her D-Mic and sang. This time, she focused everything she had into her legs. Power suddenly surged through her like a mother protecting her child. Sigils spread beneath her feet and launched her forward. She crashed through the deck glass, shattering it as she dropped into the chamber below.

Reina landed in front of her team, staring directly at the Level 4 CODA. Her sigil under her boots allowed her to float slightly above ground.

Its shell shifted. Holes opened across its surface.

Beams of light gathered inside, preparing to fire.

Reina started to invoke her Ars Aria when a shout rang out.

“I fixed it!”

The image flickered.

The Level 4 vanished before the laser reached her.

Smoke curled upward as the simulation dissolved.

Then it happened.

A roar erupted from within the fading mist.

This was no Level 4.

The roar was deep and ancient. The moment it hit, the entire chamber shook and everyone inside felt the impact. Something in that sound was wrong, powerful in a way none of them could name. Even after the mist vanished, the vibration stayed inside them.

A cold, heavy silence followed.

Reina and Takeshi spoke at the same time, even though they were far apart.

“Level… five…?”

The chamber went completely still.