A tense silence stretched between them, thick and suffocating like the heavy fog that clung to the mountain paths outside. Aiko's eyes, sharp and scrutinizing, bore into Tsuna as if searching for the deception hidden within his words.
"...You're saying one of our own betrayed us?" she repeated, her tone steady, yet something in her stance stiffened.
Tsuna nodded. "Yes. That demon wasn't acting alone—someone from your station led it here."
A muscle in Aiko's jaw twitched. The others in the group exchanged uneasy glances, but it was clear that not everyone was willing to accept such a claim.
A loud scoff cut through the quiet. "That's ridiculous!"
One of the more spirited exorcists, a young man with short brown hair and a scar running down his jaw, stepped forward, eyes blazing with anger. His grip on his sword tightened as he glared at Tsuna.
"We've fought together, bled together, and survived together," he said heatedly. "There's no way one of us would betray the station and side with demons! What proof do you even have?"
Tsuna held his ground, keeping his expression neutral despite the rising hostility. "I can't name them yet. But the way the demon fought, the way it ambushed us, it knew too much about the station's operations. Someone inside is feeding them information."
Aiko folded her arms, her lips pressing into a thin line. "And you expect me to just take your word for it? You're an outsider, Sawada. You've barely been here a day."
Tsuna exhaled slowly. He had expected resistance—of course they wouldn't believe a complete stranger over comrades they had known for years.
But he wasn't empty-handed.
"If you won't take my word for it, then take a look at this."
He reached into his coat and pulled out a worn, dust-covered booklet. The others instinctively tensed, but Aiko's brows furrowed in recognition as Tsuna held it up.
"That's…" Aiko's voice trailed off.
"A record ledger," Tsuna confirmed. "I found it in the room i met the demon earlier, tucked away behind a stack of newer logs it was also something the demon was looking through when I entered the room." He flipped open the brittle pages, revealing rows upon rows of names, dates, and notes scrawled in old-fashioned script. "It's a log of every exorcist who has ever served at this station—going all the way back to its founding."
Murmurs spread through the group. Some stepped closer, peering over Tsuna's shoulder.
"The founding?" someone repeated in disbelief.
"That station's been here since the Edo period," another exorcist muttered. "There's no way a record that old should still be here…"
Aiko hesitated, then reached for the book. As she skimmed through the pages, her frown deepened.
"These are legitimate records," she admitted, though her tone remained wary. "But what does this have to do with your claim?"
Tsuna held up another object—this time, a small, lacquered wooden tag, darkened with age and cracked at the edges. Strange markings were carved into it, some worn away with time.
"I found this hidden inside the log," he explained. "At first, I thought it was just a nameplate or an old warding charm, but…" He turned it over, revealing a recent inscription scratched hastily into the back.
Aiko's eyes widened. "That's… an incantation."
Tsuna nodded grimly. "A binding spell. And it's not just any spell—it's a pact sigil. Someone used this to form a contract with a demon."
The exorcists around them stiffened, the air in the room turning heavier. The scarred exorcist, who had been the most vocal in opposing Tsuna, took a step back.
"That can't be…" he muttered, his earlier anger now replaced with uncertainty.
Aiko inhaled sharply, flipping through the ledger once more. She turned to the most recent pages, then to the very first entry recorded at the station's founding. Her eyes darted between the names, scanning the inked kanji with growing unease.
"This log… it's been meticulously kept," she murmured. "From the very beginning, every exorcist who ever served here was recorded. But…" She stopped, her fingers tightening around the pages.
Tsuna nodded. "There are names missing, aren't there?"
The room fell into stunned silence.
Aiko swallowed. "Yes."
The missing records weren't just clerical errors. They were deliberate omissions—proof that someone had been erased from history. Someone who should have been recorded, but wasn't.
Someone who had made a pact with demons.
"…Then that means…" one of the exorcists started, voice shaky.
Tsuna looked them in the eye, his expression firm. "This betrayal didn't start today. It's been in motion for years."
Aiko's grip on the old ledger tightened. Her mind raced, sifting through the implications of what she had just read, what she had just seen. The pact sigil in Tsuna's hand carried a demonic presence—not just any presence, but one she recognized.
The same energy that had been lingering around the station for weeks.
She sucked in a breath, her throat dry. Could it really be…?
No.
She didn't want to believe it.
Tsuna was an outsider, and despite the evidence, despite the unease gnawing at her, she refused to simply accept that someone she had fought beside—someone she trusted—was capable of betraying them all.
"This sigil…" Aiko muttered, her fingers grazing the worn surface, the faintly carved incantation. "The demonic energy here—it's the same as the one that's been attacking the station."
A ripple of alarm passed through the other exorcists. Even the most skeptical among them had gone rigid, their expressions darkening.
"But," Aiko continued, her tone measured, "that doesn't prove that this sigil belongs to one of our own."
Tsuna frowned slightly, but he wasn't surprised by her reaction. Of course she would want to find another explanation. He could see the internal conflict in her eyes—the way her logical side told her one thing, while her heart wanted to reject it completely.
"I get it," he said. "It's not easy to accept that one of your own might have turned against you. But we can't ignore the facts. You just admitted the energy is the same. It's connected to the attacks on this station."
Aiko's jaw tightened. "Yes… but the demon that's been leading the attacks—its energy is all over the outer areas. We've been fighting it for weeks. But you're telling me that when you investigated the records room, a high-level demon was inside the station?"
"That's exactly what I'm saying."
A murmur spread through the gathered exorcists.
"That shouldn't be possible," one of them said. "Even with the barriers weakened, something that strong would've been detected the moment it crossed into our grounds."
Aiko clenched her fists. "The barriers… I knew they had weakened, but I thought the worst that could happen was minor possessions—humans who were still tethered to their own consciousness, able to slip past the detection wards."
Her stomach twisted.
She had assumed that was the only breach.
That was her mistake.
A high-ranked demon—not just one of its pawns, but something powerful—had slipped inside undetected. And she hadn't even realized.
"That's not all," Tsuna said, flipping through the old ledger again. "The missing records in here—they don't just stop at a single exorcist. There are gaps. Entire periods where certain names should be listed but aren't. Whoever's behind this has been covering their tracks for years."
Aiko took the book from him, scanning the pages.
She knew the history of this station well. She had studied its records as part of her training. But now that she was looking at the full picture…
There were gaps.
Names she expected to see simply weren't there.
The scarred exorcist who had initially lashed out at Tsuna stepped forward, his expression grim. "…Are you saying this traitor has been here for years?"
Tsuna's gaze flickered toward him. "Or they were here, left, and came back."
A tense silence settled over the group.
Aiko's mind reeled. If Tsuna was right, then this wasn't just a recent betrayal. Someone had embedded themselves deep within their ranks—long enough to learn the station's weaknesses, its inner workings, and how to dismantle it from the inside.
And that meant…
The demon attacks weren't just random assaults.
They were coordinated.
"We need to find out who's behind this," Tsuna said firmly. "And we need to do it fast."
Aiko nodded slowly, though doubt still lingered in her heart. "Then we investigate. But until we have undeniable proof, I refuse to point fingers at my own comrades."
Tsuna didn't argue. That was enough for now.
One of the exorcists spoke up hesitantly. "Where do we start?"
Aiko shut the ledger with a decisive snap. "We start with the barriers."
She turned to one of the older exorcists, a woman with graying hair who had been tending to the station's defensive measures.
"I need a full report on the integrity of our wards," Aiko ordered. "Check for any subtle tampering—anything that might've let something big slip through without setting off alarms."
The woman nodded and immediately left to carry out the task.
Next, Aiko turned to Tsuna. "You said the demon you fought in the records room spoke to you, right?"
Tsuna nodded. "Yeah. It called me an 'inconvenience' and tried to kill me before I could find something."
Aiko's eyes narrowed. "Then that means it knew you were a threat before you even found the ledger."
Tsuna frowned. "You think someone told it I was snooping around?"
"It's possible."
Which meant that, even now, the traitor might be watching them.
Aiko turned to the remaining exorcists. "From this moment on, no one moves alone. We work in pairs at minimum. Anyone caught acting suspiciously will be questioned."
She paused before adding, "…And if anyone has reason to believe they've been manipulated or forced into something by an outside force—now is the time to speak up."
Silence.
No one stepped forward.
Aiko exhaled through her nose. "Alright then. Tsuna, you're with me. We're going back to the records room."
Tsuna blinked. "Again?"
"If that demon was willing to risk exposure just to keep you from finding something, then there's a chance you missed something important."
He couldn't argue with that logic.
The two of them moved out, heading down the dimly lit corridors of the station. The air was thick with tension, and Tsuna could feel Aiko's gaze occasionally flickering toward him.
She still didn't fully trust him.
That was fine.
But she was willing to work with him.
And right now, that was enough.
As they approached the entrance to the records room, Aiko's hand moved to her sword hilt, her grip firm.
Tsuna pushed open the door—
—and stopped short.
The room was empty.
--------------------------------------------------------
Tsuna frowned, stepping inside as the scent of burnt paper and wood filled his nose. Just earlier, this place had been intact—an old office filled with countless documents, ledgers, and records. Now, all that remained were smoldering ruins.
Someone had been here after he left.
Aiko followed closely behind, her sharp gaze sweeping over the destruction. She had insisted on coming back, hoping to uncover something Tsuna might have overlooked, but now they were faced with nothing but charred remains.
Her fists clenched at her sides. "Damn it… They worked fast."
Tsuna crouched near the remains of a bookshelf, running his fingers through the ash-covered floor. "Not just fast. They knew exactly what to burn."
Aiko's lips pressed into a thin line. "They weren't just covering their tracks… they were erasing something."
The severity of her words wasn't lost on Tsuna. This wasn't just about hiding a single act of betrayal—whoever did this wanted to wipe out something important. But what?
His eyes darted across the room, searching for anything that had been left behind. If the arsonist was in a hurry, there was a chance they missed something. His gaze landed on a section of the floor near the far wall, where the fire hadn't completely spread.
Something metallic glinted faintly among the debris.
Tsuna moved toward it, brushing away the ash until his fingers touched a small, warped piece of metal. The moment he made contact, a faint pulse of warmth spread through his fingertips.
His stomach dropped. Demonic energy.
"Aiko."
She was already beside him before he even called. Her eyes narrowed as she reached for the object, carefully turning it over in her hand. The engravings on its surface were partially melted, but traces of an intricate design were still visible.
Aiko exhaled sharply. "This... this is a charm fragment."
Tsuna's brows furrowed. "A charm?"
She nodded, her grip tightening. "Not from our station. But I recognize the structure—this was part of a barrier seal."
That immediately set off alarms in Tsuna's mind. "A barrier?"
Aiko's jaw tensed. "But it's been altered." Her voice grew colder. "Instead of repelling demons, this was modified to conceal them."
The realization hit Tsuna like a punch to the gut. That explained how a demon managed to infiltrate the station without triggering alarms.
"That's why you didn't notice," Tsuna murmured.
Aiko's fingers curled around the charm. "...I thought, at worst, minor possessions had slipped through. That some humans, still retaining just enough willpower, had bypassed the barriers by suppressing their demonic energy. But I was wrong."
Her eyes darkened as she stared at the charm. "A high-ranked demon didn't just get in. It's been here for a while. And I had no idea."
A heavy silence settled between them.
Tsuna could feel the weight of Aiko's frustration, her anger not just at the situation but at herself. She was the one responsible for protecting this place, yet the enemy had been moving right under her nose for who knows how long.
He sighed. "It's not your fault. Whoever did this knew exactly how to avoid detection."
Aiko scoffed. "That doesn't change the fact that they succeeded."
She exhaled, forcing herself to refocus. "But there's something else. This fragment—it still contains a residual signature."
Tsuna's eyes sharpened. "A signature?"
Aiko nodded. "Traces of the pact—a connection left behind by the one who modified this charm."
Tsuna's stomach clenched. "And?"
Aiko hesitated for only a second before speaking. "...It matches the energy of the demon we've been fighting for weeks."
A cold weight settled in Tsuna's chest.
The demon he encountered in the records room—it wasn't a random intruder. It was tied to the same force that had been attacking this station for a while now.
Aiko's grip on the charm tightened. "I can't say for sure if it's the same demon, but the energy is too similar to be a coincidence."
Tsuna exhaled slowly. That meant their enemy wasn't just inside the station.
They had been part of it for years.
His gaze darkened. "Then we have a lead."
Aiko straightened, a fire burning in her eyes. "And we're going to follow it."
--------------------------------------------------------
Despite the destruction of the office, Aiko and Tsuna still combed through the ruins, searching for any remnants of evidence—anything that could tell them what the demon had been doing here.
But no matter how much they searched, they found nothing.
It was frustrating. Even though Aiko knew the chances were slim, she had hoped for something—some overlooked trace, a hidden clue buried beneath the ashes. Yet, with how thoroughly the room had been wiped clean, it was clear the enemy had left nothing behind.
Aiko clenched her fists. "Tch. They were too fast."
Tsuna glanced at her. "It means they're scared."
Aiko's jaw tightened. Maybe. But right now, that knowledge didn't make her feel any better.
Before she could reply, footsteps echoed down the hallway.
A group of exorcists entered the burnt-out office, their presence filling the space with a heavy, commanding air. At the front of the group stood a middle-aged man with a scar running down the side of his neck, his rugged features hardened by years of experience. His sharp eyes immediately landed on Aiko and Tsuna.
"Aiko," he greeted gruffly, his tone edged with urgency. "We've finished securing the perimeter."
Captain Ryuji Nakamura—one of the senior exorcists stationed here. Unlike Aiko, whose leadership was more tactical and refined, Nakamura was known for his no-nonsense approach, a veteran who had survived far too many battles against demons.
Behind him were two more exorcists, both clearly seasoned fighters.
The first was Shiori Takagi, a sharp-eyed woman in her early thirties, her short black hair tied back in a low ponytail. Though her demeanor was calm, the way she held herself screamed efficiency and authority.
The second was Tetsuo Maeda, a tall man with a broad frame, his uniform slightly disheveled but his stance steady. Unlike the others, his expression carried a hint of fatigue, though his eyes remained alert.
Standing behind them was another group—five younger exorcists, the same ones who had helped Tsuna earlier when he was still recovering from his injuries.
This squad of five consisted of:
Keita Yamazaki, a level-headed swordsman and the de facto leader of the small unit.
Haruto Fujimura, a short but fast exorcist specializing in barrier reinforcement.
Nao Miyoshi, a quiet girl who mainly focused on healing techniques.
Toru Ishikawa, a hot-headed fighter who was eager to prove himself.
Ayaka Sasaki, a twin-blade user with an uncanny ability to sense demonic presences.
This was at least the introduction each of them gave to Tsuna earlier when they introduced themselves to him during the time Tsuna was still very much weak and recovering from the battle that drained his stamina severly.
Nakamura crossed his arms, his expression grim. "The area around the station has been cleared. Any remaining possessed humans have been taken care of. Those who were exorcised and left unconscious have been sent to the medical ward of the affiliated hospital nearby."
Aiko nodded. "The one under government jurisdiction?"
"Yeah. To keep up the cover story, they've labeled it as a mass outbreak of an unknown illness," Shiori added. "Most of the civilians have already been convinced it's nothing more than a strange epidemic."
Tsuna exhaled. So that's how they kept the public unaware of what was really happening.
"Good," Aiko muttered. "At least that part is handled."
With the lack of physical evidence in the burned room, Aiko knew that their best bet was to question everyone in the station. The only way to catch a potential accomplice was to scrutinize every alibi, every movement, and every inconsistency.
As the head of the station, she wasted no time in calling for a full assembly.
The exorcists stationed here—around thirty to fifty in total—were gathered in the main hall of the base. Some were still out in the city, continuing their missions to exorcise remaining possessed civilians, but those who were available had arrived quickly. A tense energy filled the air as they stood in formation, their eyes locked onto Aiko, waiting for her to speak.
Tsuna stood beside her, watching the group. Many of the exorcists had been here for years, working and fighting alongside each other. The idea that one of them had betrayed the station was something none of them wanted to believe.
Aiko took a deep breath and stepped forward.
"I'll be direct," she said, her voice sharp and unwavering. "Someone here—or someone we trust—is working with demons."
A ripple of murmurs spread through the crowd. Some exorcists stiffened, while others exchanged uneasy glances.
"We don't have solid proof yet," Aiko continued, "but we know the enemy moved too precisely. They infiltrated our station, burned evidence, and planted a sigil that had been active for a long time. This isn't random—it's been in motion for years."
The crowd fell into a heavy silence.
"Because of that," she said, her tone grave, "we will be checking every single person's alibi. If you were in the station during the attack, we need to confirm where you were and what you were doing."
A tense pause.
"Those who were outside on missions, we will verify your reports later."
There was no room for argument.
With that, the questioning began.
--------------------------------------------------------
The questioning continued, and the list of those without alibis slowly came together. Each case was different, though one thing was clear—none of them could account for their whereabouts during the crucial moments of the attack.
Aiko's gaze swept over the group that remained under scrutiny, her sharp eyes watching for even the slightest shift in body language.
Captain Ryuji Nakamura stood firm with his arms crossed, his rugged face unreadable. A veteran exorcist and one of the strongest in the station, Nakamura was someone others naturally looked up to. His issue, however, was that he had arrived late to the battle. He claimed to have been doing a security sweep on the outer perimeter, ensuring that no possessed civilians slipped past their defenses. Yet, no one could verify seeing him until after the attack was already in full swing.
"Why didn't you report in?" Aiko asked.
"I tried," Nakamura replied evenly. "But my communicator was jammed. You know how unpredictable demonic interference can be."
That was true—but it was also too convenient.
Next to him, Shiori Takagi stood with her arms folded. Tall and composed, she was known for her sharp tactical mind. Unlike Nakamura, who had been outside, Shiori had been within the base during the attack, yet she hadn't been seen in any of the major defensive positions. When pressed, she admitted she had been in one of the smaller archives, reviewing classified files on past demon encounters.
"I was looking into cases that might relate to our recent enemy," she explained. "By the time I realized something was wrong, the halls were already swarming with possessed civilians, and I had to take a longer route to avoid them."
Again, it sounded reasonable. But why was she alone?
Tetsuo Maeda, a broad-shouldered man with a permanent scowl, let out a grunt when his name was called. He had been unaccounted for until after the battle had begun. His excuse? He had been in the underground storage area, retrieving extra supplies for the defensive teams. But again—no one had seen him until much later.
"If I was a traitor, why would I bother fighting so damn hard during the attack?" he snapped.
Aiko ignored the outburst, jotting something down on her notes.
Then there was the five-person exorcist squad Tsuna had encountered earlier—Keita Yamazaki, Haruto Fujimura, Nao Miyoshi, Toru Ishikawa, and Ayaka Sasaki.
Their case was particularly tricky. They had been out on a mission and were the only team that had returned right before the attack. Given the timing, it was suspicious, but their reasons were at least plausible.
Keita, the unofficial leader of the squad, stepped forward. "We finished our mission and were heading back as scheduled. We didn't know what was happening until we saw the possessed civilians swarming the outer station walls."
"But no one can verify where you were before that," Aiko pointed out.
The squad exchanged glances. They had no solid proof—only their word.
And then there was the final suspect.
Vice Chief Osamu Hayashi.
Thin, elderly, and always calculating, Osamu had been with the station longer than nearly anyone else. He rarely fought anymore, instead overseeing strategy and long-term operations.
"I was in my quarters," he said simply. "At my age, I am not as quick to respond to emergencies as the younger exorcists."
His reasoning was understandable—but there was something unsettling about it.
Aiko tapped her pen against her clipboard, her expression unreadable.
They had nine people, each with a missing gap in their timeline. Some had reasonable explanations. Some were harder to believe.
But one of them—at least one—had to be lying.
A heavy silence hung in the air.
And then, the accusations began.