"I can think of several reasons, none of them good." Tengen met his gaze steadily, pulling them back from the abyss of speculation to concrete analysis. "Someone building an army. Someone studying them for weaknesses or capabilities. Someone who needs them alive for purposes we haven't discovered yet."
"You think she's collaborating with demons?"
"I think she's manipulating them for goals that don't align with Corps objectives." Tengen shifted position, unconsciously demonstrating basic sword stances despite his disability. "Her combat techniques bother me too. I've studied every documented breathing style in Corps history. They all channel energy through specific muscle groups and sword movements designed for maximum cutting efficiency."
Tanjiro's mind raced through his observations, pieces clicking into place like a puzzle he'd been unconsciously solving. "Her Breath of Lies is supposedly new—"
"Traditional breathing styles enhance physical capabilities." Tengen's demonstration showed the flowing connection between breath, stance, and sword work. "Hers seems designed to influence minds rather than cut flesh."
The observation crystallized Tanjiro's vague unease into sharp-edged fear. Everything about Akira's fighting style had felt wrong from the beginning—not ineffective, but fundamentally different in purpose and execution.
"You think she's using some form of hypnosis?"
"I think she's using techniques no legitimate demon slayer would develop." Tengen's voice carried absolute certainty. "The question is where she learned them, and from whom."
"Could she have learned from demons themselves?"
"That's exactly what I'm afraid of."
---
The admission hung between them like a suspended blade. If Akira had learned her techniques from demons, it suggested collaboration that went far beyond simple relocation efforts—it implied a fundamental betrayal of everything the Corps stood for.
The weight of that possibility settled over Tanjiro like a physical burden, but it was nothing compared to what came next.
"There's something else," Tanjiro said reluctantly. "Nezuko's been having nightmares since Akira arrived."
Tengen went completely still, his remaining eye fixing on Tanjiro with laser intensity. The change in his demeanor was immediate and alarming—like watching a predator catch scent of its quarry.
"What kind of nightmares?"
"She won't talk about them, but she's been waking up with scratches on her bedframe. Deep gouges like claw marks." Tanjiro's voice dropped to barely above a whisper. "And yesterday I caught her staring at her reflection like she didn't recognize herself."
"Kamado." Tengen's voice carried urgent concern that made Tanjiro's blood run cold. "Your sister represents something unprecedented in demon-human relations. If someone wanted to study or exploit her transformation, she'd be an obvious target."
"You think Akira is targeting Nezuko specifically?"
"I think anyone with an interest in demon-human transformation would find your sister fascinating. And that terrifies me more than any demon I've ever faced."
The protective fury that rose in Tanjiro's chest felt familiar, comforting in its simplicity. This was territory he understood completely—protecting Nezuko was his primary purpose, his driving motivation, the north star that guided every decision.
---
"What do we do?" he asked, surprised by the steadiness of his own voice despite the rage building beneath his calm exterior.
"We gather evidence that will convince Ubuyashiki and the other Hashira." Tengen began organizing his documents, his movements carrying the efficiency of a man accustomed to life-or-death planning. "Suspicions won't be enough to act against someone with her apparent record and demonstrated abilities."
"What kind of evidence?"
"Proof of her deception. Documentation of her real activities. Witnesses who can testify to her actual behavior during missions." Tengen counted points on his fingers. "We need to catch her in the act of whatever she's really doing."
"That sounds dangerous."
"Less dangerous than letting her continue unopposed." Tengen fixed him with a stare that carried battlefield experience and hard-won wisdom. "Are you prepared for what we might discover?"
The question demanded honesty—not just about his courage, but about his willingness to confront ugly truths about someone he'd been ordered to trust. About potentially discovering that the Corps itself had been compromised, that his faith in their leadership might have been misplaced.
"I have to be. Too many people could get hurt if we're right."
"And if we're wrong?"
"Then I'll apologize and accept whatever consequences come from investigating a fellow Hashira." Tanjiro met Tengen's gaze steadily. "But I won't ignore my instincts when they're screaming warnings this loudly."
Tengen nodded with approval that felt like validation from a teacher recognizing growth in a student.
---
"Why are you willing to help me with this?" Tanjiro asked, needing to understand what drove Tengen to risk so much on the suspicions of a younger Hashira.
"Because I've seen too many good people die because someone ignored warning signs." Tengen's voice carried the weight of losses that had shaped him, ghosts that haunted his decisions. "My wives, fellow Hashira, innocent civilians—all because someone in authority decided to trust appearances over evidence."
"Even if it means going against a fellow Hashira?"
"Especially then. The higher someone's position, the more damage they can do if they're compromised." Tengen leaned back against his cushions, but his posture remained alert. "I have a responsibility to train and protect younger Corps members. That includes protecting them from threats within our own ranks."
"This feels like betrayal."
"It feels like duty. Sometimes they're the same thing."
The harsh truth settled into Tanjiro's bones like winter cold. Leadership meant making impossible choices. Meant prioritizing protection over comfort, truth over loyalty. Meant accepting that sometimes the greatest threats came from those who should have been allies.
Tengen reached into his clothes and produced a small wrapped package. "Communication methods from my shinobi days. Discrete signals, coded messages. Use them if you discover anything urgent that can't wait for our next planned meeting."
"What's our timeline?"
"As short as possible. If she's building toward something, every day we delay gives her more opportunity to complete her plans." Tengen stood with fluid grace. "Watch her carefully during your next mission. Document everything. Trust your instincts above all else."
---
Tanjiro tucked the package away, feeling its weight like a stone in his pocket—a tangible reminder of the dangerous path he was choosing to walk.
"And if my instincts tell me she's dangerous?"
"Then we stop her before she can hurt anyone else." Tengen walked him toward the door, their footsteps echoing softly in the corridor. "Your nose has never led you wrong before, Kamado. Don't start doubting it now."
As they reached the main entrance, Tengen paused with his hand on the door frame. The gesture seemed casual, but Tanjiro caught the subtle tension in his shoulders—the alertness of someone checking for threats even in his own home.
"One more thing. Be careful who you trust with this information. If Akira has allies within the Corps, careless words could get you killed."
"You think there might be others?"
"I think someone with her apparent capabilities and resources didn't develop them in isolation." Tengen's eye glittered with cold calculation. "Assume you're being watched. Assume your conversations are being monitored. Assume nothing until we know the full scope of what we're dealing with."
Tanjiro stepped into the night air, carrying both renewed purpose and a heavy heart. The mist had thickened while they'd talked, turning the familiar path back to headquarters into a maze of shadows and uncertain footing.
Perfect weather for secrets and conspiracies.
The investigation was no longer a private concern born from vague unease. It had become a mission that could determine not just his own survival, but the future of the Corps itself. And somewhere in the darkness ahead, Akira was pursuing goals that required demons to remain alive and his sister to question her own humanity.
Tanjiro pulled his haori tighter against the cold and began the careful journey home, every sense alert for threats that might already know he was coming.