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English
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Published:
2024-10-08
Updated:
2026-03-30
Words:
7,803
Chapters:
7/?
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The Exchange

Summary:

The deal is simple: one life for another.

The Port Mafia wants Dazai Osamu back.

Mori calls it an exchange.

Dazai calls it a mistake.

As the past closes in and the line between ally and enemy blurs, the Agency begins to realize the truth—

The “Demon Prodigy” never really disappeared.

And getting him back might cost more than anyone is prepared to pay.

 

Marked T for swearing, and canon typical violence/dark themes.
Manga Spoilers through to the end of Part 1

Chapter 1: Chapter 1

Summary:

This is the March 16th 2026 Re-write :)
The chapter has been significantly changed in terms of quality and detail; however, the gist remains the same.

Chapter Text

Dazai had known from the start it would be him.

Even if Yosano were still an option, Mori would never pass up the opportunity to reclaim his Demon Prodigy. Sentiment had never stopped the man before, and it certainly wouldn’t start now.

Still… It was a little unfortunate.

Somewhere along the way, the Agency had stopped feeling like a convenient hiding place and started feeling something closer to home. The kind of place where people trusted him—oddly enough.

But the tripartite system had to remain intact. If the balance collapsed, far more people would suffer than just one former mafioso returning to where he came from.

A small price to pay.

He wondered, briefly, what Oda would think.
Dazai had tried. Really tried.
Tried to do things the “right” way, the way Oda had asked.

Whether he had succeeded… well.
That was probably still up for debate.

“Dazai-san… who do you think will be chosen?” Atsushi asked timidly.
Roused from his thoughts, Dazai turned toward his mentee, plastering his usual carefree smile across his face.

“I don’t know, Atsushi-kun,” he said lightly. “But I’m sure whoever is chosen, everything will turn out fine.”

Dazai glanced over at Ranpo.
Of course he’d noticed.
Ranpo met his gaze and gave the faintest nod—barely there, invisible to anyone who wasn’t looking for it.

Ah. So the great detective had reached the same conclusion.

That was reassuring, in a way. It meant Dazai’s prediction was probably correct.

Still, it was better this way. If Mori took anyone else, the balance between the organizations would tilt in ways far more dangerous than one prodigal executive returning home.

And besides…
Dazai had never really escaped the Mafia.
He had only stepped outside it for a while.

“Atsushi,” Kunikida said, pushing his glasses up the bridge of his nose, “we’re all worried. And aside from possibly Ranpo, none of us have any clue who Mori might choose.”
He gestured toward the stack of paperwork.
“So please try to finish your work. Efficiency is key. The more we get done now, the better prepared we’ll be once we start taking cases again. I refuse to let this un-ideal disorganization spiral.”

It was obvious to Dazai that Kunikida wasn’t truly concerned about paperwork—or his precious ideals—right now. He was coping the only way he knew how: clinging to routine while realizing he will soon lose one of his coworkers.

~~~Time Skip Brought to you by our sponsor: Karl the Raccoon~~~

After a tense lunch at the café, the ADA returned to the office to prepare for their meeting with the Port Mafia. The tension in the room had become almost suffocating.

The President cleared his throat.
“Mori, along with two Port Mafia executives—Nakahara Chuuya and Ozaki Kouyou—will be joining us within the next half hour to discuss who they’ve selected to join the Port Mafia and uphold our end of the agreement.”

His gaze shifted briefly toward Dazai.

“No matter who is chosen,” Fukuzawa continued, “I want you all to remember that we are a family here. Because of the truce, you will still be able to stay in contact and see each other again. I deeply regret that it has come to this.”
His voice softened slightly.
“You are all the strongest and bravest people I know—”

A knock interrupted him.

“Come in.”

“Good afternoon, Fukuzawa. I hope I’m not interrupting anything important,” Mori greeted smoothly.

Dazai noted immediately that Mori wasn’t wearing his usual black coat. Instead, he had chosen one that was only slightly less formal.
A small detail.
Which meant it probably wasn’t one at all.
Mori never did anything without a reason.

“Good afternoon, Mori,” Fukuzawa replied calmly. “You are not, although you are considerably early.”
“Sorry about that,” Mori said, not sounding sorry in the slightest. “Unfortunately, I have another meeting afterward that I’m unable to reschedule.”

His gaze drifted toward Yosano.

She tensed instantly, grabbing a cleaver from the table beside her.

“What a shame,” Mori crooned. “It seems I won’t be getting my Angel of Death back today.”
At the taunt, Yosano stepped forward with a low growl, clearly ready to murder him. Ranpo quickly moved in front of her.

Dazai also rose silently, shifting his weight carefully onto his uninjured leg.
Without the ability to physically attack, Yosano opened her mouth—clearly ready to verbally tear Mori apart—but Fukuzawa cut in smoothly.
“We are here for a business meeting to discuss the truce and the transfer of one of my employees,” he said evenly. “Nothing about that gives you the right to deliberately provoke them.”

“Speaking of which,” Kunikida interjected stiffly, gripping his notebook, “our meeting room is right this way.”
He turned and led them down the hall toward the conference room, his knuckles white around the notebook.

The conference room felt smaller than usual.

Too quiet.

The ADA took their seats on one side of the long table while the Port Mafia settled across from them. Mori sat comfortably at the head of his side, hands folded as if this were nothing more than a polite business meeting.

Chuuya leaned back in his chair, hat tipped low over his eyes, one leg crossed over the other. Kouyou sat beside him with perfect posture, her sleeve hiding her expression.
Dazai took his seat across from them.

Chuuya’s gaze flicked up for the briefest moment.

Their eyes met.

There was no surprise there. No smug satisfaction either.

Just understanding.

Ah.
So Chuuya had figured it out too.
Of course he had.

Dazai leaned back in his chair, folding his hands behind his head with an exaggerated sigh.
“Well then,” he drawled. “Shall we get this over with? All this tension is terrible for my delicate constitution.”

“Dazai-san…” Atsushi whispered from beside him.
Dazai didn’t look over.

Across the table, Mori smiled faintly.
“You always were impatient, Dazai-kun.”

His eyes drifted across the room, taking in each member of the Agency one by one. Lingering just long enough to make the silence stretch.

Kunikida’s grip on his notebook had gone rigid.

Tanizaki sat unnaturally still.

Kenji looked confused, glancing between the adults.

Yosano leaned back in her chair, cleaver resting against the table like a quiet threat.

Ranpo, meanwhile, had already opened a bag of snacks.

Crunch.

The sound echoed far louder than it should have.
“Ranpo,” Kunikida hissed.
Ranpo didn’t even look up.

“You’re all overthinking it,” he said around a mouthful of chips. “The answer’s obvious.”

Atsushi’s head snapped toward him.
“What—?”

Mori chuckled softly.
“Well, well. As expected of the great detective.”

The room tightened.

Dazai could practically feel Atsushi turning toward him.
He still didn’t look.

“President Fukuzawa,” Mori continued smoothly, “as per our agreement, the Port Mafia will be selecting one member of the Armed Detective Agency to join our ranks in order to maintain the balance of the tripartite system.”
He steepled his fingers.
“The choice was… quite simple, really.”

Across the table, Chuuya exhaled through his nose, muttering something under his breath.
Dazai caught it anyway.

“Dumbass.”

Affectionate, almost.
How nostalgic.

Mori’s gaze finally settled.
Right on him.
There it was.
The moment the room realized it.

Atsushi inhaled sharply.

Kunikida froze.

Even Yosano’s hand tightened around the cleaver.

Dazai only smiled.
Carefree.
Unbothered.
Exactly the mask they were used to seeing.
“Well?” he said lightly. “Don’t keep everyone in suspense, Mori-san.”
Mori’s smile widened.
“Our selection is—”