The moon hung low over Seiki Academy, its pale light spilling across the courtyard like a silent witness. The message on Kaito's desk had long since burned away, but the words echoed in his mind like a drumbeat:
Your vow will not save you. The hunger always wins. Come to the Undercroft if you want the truth.
He hadn't told Hina or Riku about it yet. Not fully. How could he? The very idea of the Undercroft—a place whispered about in half-muttered rumors—felt like stepping into a trap. But he couldn't ignore it.
The figure from the Forbidden Wing had recognized the Void within him. It had spoken to him, as if they were connected by some hidden thread.
He had to know why.
Hina, however, was not one to let him brood silently. She sat on the edge of his bed, arms folded, her fiery aura flaring faintly even in her relaxed state.
"You're thinking about going, aren't you?" she said bluntly.
Kaito didn't look at her. "If it's connected to the disappearances… to the Void… I need to see for myself."
"You're not going alone," she replied without hesitation.
Riku, who had been quietly reading in the corner, closed his book. "Nor should you. The Undercroft is said to be beneath the oldest part of the Academy. It's heavily warded. If this is a trap, you'll need someone who can disarm it."
Kaito finally turned to them. "I didn't want to drag you into this."
Hina smirked. "Too late."
Riku stood, adjusting his glasses. "We leave after curfew. The tunnels connect near the northern garden. Few patrols pass that area at night."
The Descent
The northern garden was quiet, bathed in the soft glow of enchanted lanterns. The trio moved swiftly, their footsteps muffled on the stone paths.
Riku led them to a crumbling statue of the Academy's founder—a stern-faced warrior whose outstretched hand pointed toward the mountains.
"Here," Riku said, pressing his hand against a hidden panel on the statue's base. Threads of his Shirabe Seiki slid into the ancient mechanism, unraveling its lock.
With a low rumble, a section of the garden floor shifted, revealing a narrow staircase spiraling down into darkness.
Hina peered into the abyss. "Creepy."
Kaito swallowed hard. The Void inside him pulsed in response to whatever lay below, like a predator sensing another.
"Stay close," Riku instructed as they descended.
The air grew colder, damp with the scent of earth and something faintly metallic. The stone walls were carved with ancient glyphs that flickered weakly, as if barely alive.
They reached a massive underground chamber where several tunnels branched out like veins. At the center stood a sealed door covered in writhing sigils—unlike any they had seen before.
Kaito stepped closer. The Void within him reacted violently, pulling at him, urging him to open the door.
"This is it," he whispered. "The Undercroft."
But before they could move further, a voice cut through the still air.
"I was wondering when you'd come."
The trio spun around.
Standing in the shadows was Rei, the pale boy with piercing blue eyes. His usual calm smile was gone—replaced by something sharper, colder.
"Rei?" Hina frowned. "What are you doing here?"
Rei stepped forward, his aura flaring—a strange mix of Shirabe precision and something darker, more primal.
"I'm here because the Undercroft doesn't welcome just anyone," Rei said, his tone almost mocking. "It chooses those who are… marked." His gaze locked on Kaito. "Like you."
Kaito stiffened. "You know about the Void?"
Rei's smile widened slightly. "I know more than you think. That figure you saw in the Forbidden Wing? It's part of the truth this Academy hides. But you're not ready for it."
"And you are?" Riku asked, threads twitching, ready for combat.
"I've been preparing for this far longer than you," Rei replied. "The question is, will you get in my way?"
The tension snapped like a bowstring.
The Battle in the Tunnels
Rei's Seiki flared, threads of shimmering blue light shooting outward. Unlike Riku's controlled lattice, Rei's threads moved like living serpents, weaving intricate traps that tightened the more you struggled.
Hina leapt forward, fists blazing. "We're not backing down!"
Her punch collided with Rei's threads, scattering them briefly, but he recovered instantly, redirecting them to bind her arms mid-air.
"You're strong," Rei said casually, "but you lack precision."
Riku countered, his own threads slicing at Rei's in a delicate dance of manipulation. The air shimmered with the clash of Shirabe mastery.
Kaito stood frozen for a split second, the Void within him screaming to be unleashed. He could feel Rei's energy—it was familiar, almost resonating with his own darkness.
Then Rei turned his gaze on him.
"Show me," Rei said softly. "Show me the hunger."
That single phrase broke Kaito's restraint.
Void tendrils exploded from him, black and writhing, consuming the dim light around them. The tunnels groaned under the pressure of his unleashed power.
Rei laughed—a short, sharp sound. "Yes… that's it!"
The battle became chaos. Rei's threads slashed through the darkness, meeting Kaito's Void in a clash that sent shockwaves through the tunnel. Hina broke free from the bindings, delivering a blazing strike that forced Rei to retreat momentarily.
But Rei was fast—too fast. His threads adapted, learning the rhythm of their attacks.
"You're reckless," Rei taunted, dodging Hina's next blow. "The Void will eat you alive before you ever understand it."
"Shut up!" Kaito roared, pushing more of his power out. Tendrils surged forward, devouring Rei's threads bit by bit.
Rei's eyes gleamed. "Good… now you're closer to the truth."
For a moment, Kaito felt the Void almost merge with Rei's energy—like two halves of the same thing. His vow strained, cracking under the pressure.
He heard a faint whisper—"Let go…"—and for a terrifying second, he almost did.
But Hina's voice cut through the haze.
"Kaito! Don't lose yourself!"
The sound of her voice anchored him. With a final surge of will, he pulled back, reining in the Void before it could completely consume him.
Rei stepped back, expression unreadable now.
"Interesting," Rei murmured. "You're stronger than I thought. But still… not enough."
Before they could strike again, Rei vanished into the shadows, his presence fading like a phantom.
Aftermath
The three stood panting in the dim tunnel, the silence heavy after the clash.
"What the hell was that?" Hina demanded, fists still trembling with residual energy.
Riku adjusted his glasses, frowning. "Rei… isn't just a rival. He knows about the Void. Maybe even shares a connection to it."
Kaito stared at the sealed door of the Undercroft. His body ached, his vow still straining from the near-break.
"He's hiding something," Kaito said quietly. "And this door… it's still calling to me."
Hina touched his shoulder. "We'll figure this out. Together."
But deep inside, Kaito knew the Undercroft held answers he couldn't ignore. And Rei… Rei wasn't just an obstacle. He was a key.
As they prepared to retreat, the sigils on the door pulsed faintly—as if awakening.
And from the darkness behind the door came a whisper—faint but clear.
"Kaito Renge… come find me."