Chapter Text
Naomi Nakahara Tanizaki had a theory.
A ridiculous, unbelievable, scandalous theory.
And the worst part?
No one believed her.
It began three days after the disastrous “spy incident.” Life at the Agency had returned to something resembling normal — if “normal” meant Dazai hanging upside down from the ceiling fan, Kunikida screaming about productivity, and Tanizaki avoiding eye contact with everyone.
But Naomi… Naomi had seen things.
The way Tanizaki’s face went bright red whenever Tachihara walked by the Agency’s door.
The way Tachihara always “dropped in” at the exact same hour every night.
The mysterious noises from Tanizaki’s locked room.
And most damning of all — the suspicious limp her brother had the next morning.
Naomi wasn’t born yesterday.
She knew exactly what was going on.
“Naomi,” Yosano said patiently, sipping her tea as Naomi paced the office floor. “We’ve been through this. They said they were working on a joint mission.”
Naomi slammed her hands on the table. “That’s what they want you to think!”
Atsushi blinked. “Wait— so you think they’re not?”
Naomi leaned closer, voice dropping to a dramatic whisper. “Atsushi-kun… they’re involved.”
“Involved?” he repeated nervously.
“Involved,” she said, nodding gravely. “Romantically. Physically. Passionately!”
Atsushi’s face turned redder than his tie. “W–WHAT?! Naomi-san, that’s—!”
“They’re both men,” Kunikida interrupted, pinching the bridge of his nose. “This is absurd.”
Naomi crossed her arms. “And? Love knows no bounds, Kunikida-san.”
Dazai, sitting nearby with a grin far too wide, clapped slowly. “I, for one, support Naomi-chan’s investigative spirit. A forbidden affair between an Agency member and Port Mafia member? How tragically poetic!”
Yosano smirked. “And very entertaining.”
“Not entertaining!” Kunikida barked. “Baseless gossip!”
Naomi pointed dramatically toward the ceiling. “It’s not gossip if it’s the truth!”
Night 1: The Second Stakeout
Despite Kunikida’s objections (and much to Dazai’s delight), the Agency found themselves once again stationed outside Tanizaki’s apartment at midnight.
Naomi crouched in the hallway, pressing her ear against the door. Dazai, Atsushi, and Kenji flanked her. Yosano sipped wine on the sofa. Kunikida stood with his notebook, muttering something about “unprofessional behaviour.”
Then it happened.
Click.
The door locked.
Naomi gasped. “There! You heard it!”
Dazai leaned forward, eyes twinkling. “Oh, I definitely heard something.”
Inside, faint sounds filtered through the door — soft voices, laughter, and something that sounded suspiciously like a groan.
Naomi’s eyes widened in horror and triumph. “See?! SEE?!”
Kunikida rubbed his temples. “Could be exercise.”
“Exercise doesn’t sound like that!” Naomi whispered harshly.
A loud thud followed by muffled words drifted out. Dazai raised a brow. “That’s either a fight or… well, not a fight.”
Yosano chuckled. “Maybe both.”
Atsushi’s face was buried in his hands. “I don’t think we should be listening to this…”
Kenji tilted his head. “Are they wrestling?”
“...In a way,” Dazai said thoughtfully.
The next morning at the Agency, Naomi marched up to her brother’s desk with the confidence of a prosecutor presenting evidence.
“Good morning, Junnii,” she said sweetly.
Tanizaki froze. “...Morning.”
He looked exhausted. His hair was slightly mussed, shirt collar wrinkled, eyes heavy-lidded. Tachihara, sitting across the room filling out a report, didn’t look much better.
Naomi’s smile widened. “Rough night?”
Tanizaki nearly choked on his coffee. “W–WHAT?!”
Yosano, who had been observing quietly from her chair, bit back a laugh. “Oh, Naomi.”
Kunikida sighed. “Naomi, for the last time—”
But Naomi wasn’t done. She slammed down a folder full of “evidence” — timestamped photos, notes, and sound recordings from the night before.
“Exhibit A: The door locked at exactly 11:58 PM. Exhibit B: Muffled noises consistent with… activity. Exhibit C: Both suspects appear fatigued this morning!”
Tanizaki’s face turned scarlet. “N-Naomi! What are you implying?!”
“That you’re hiding something,” she said triumphantly. “And I will uncover it.”
Tachihara groaned, rubbing his forehead. “You really don’t know when to quit, huh?”
Naomi crossed her arms. “Oh, I’ll quit when you two stop acting like you’re doing paperwork at midnight.”
A long, awkward silence followed.
Tanizaki avoided everyone’s eyes.
Tachihara coughed.
Dazai’s grin could have lit up Yokohama.
“...So it is true,” Dazai said softly, practically vibrating with joy.
“Dazai—!” Kunikida snapped.
But it was too late. The room had erupted.
Kenji congratulated them warmly.
Atsushi stammered apologies for eavesdropping.
Yosano toasted them with her tea, muttering something about “finally some excitement around here.”
Meanwhile, Naomi just stood there, utterly victorious.
“I knew it,” she declared, hands on her hips. “Next time, maybe you’ll believe me.”
In their apartment, Tanizaki buried his face in his hands as Naomi hummed cheerfully in the kitchen.
“You told everyone,” he groaned. “You told the entire Agency.”
Naomi looked innocent. “I didn’t tell them, Junnii. They figured it out.”
“You led a stakeout!”
“Details, details.”
Tanizaki groaned louder. From across the room, Tachihara chuckled quietly, leaning against the counter.
“She’s kind of scary,” he said.
Naomi turned, smiling sweetly. “Scary enough to keep secrets from?”
Tachihara’s smirk faltered. “Uh… no, ma’am.”
“Good,” Naomi said, pouring herself some tea. “Because if you hurt my brother, I’ll make sure you regret it.”
Tachihara nodded slowly. “...Understood.”
Tanizaki groaned again. “Naomi…”
She smiled, taking a sip of tea. “I’m just happy you found someone, Junnii.”
He peeked up, surprised by the softness in her tone.
Her smile turned sly again. “Even if you two are really loud.”
Tachihara choked. Tanizaki turned crimson.
Naomi just hummed and walked away, mission complete.
Epilogue
The Agency was never the same.
Naomi’s “Operation Midnight Secret” became a running joke.
Yosano called Tanizaki and Tachihara “the night shift.”
Dazai claimed credit for “mentoring young love.”
And Kunikida rewrote the Agency rulebook again to ban all internal surveillance operations — specifically citing “the Naomi Incident.”
As for Naomi?
She was content knowing she had been right all along.
Her brother was in love.
Her intuition was flawless.
And she was absolutely keeping the recordings.
For “blackmail purposes,” of course.