Ranking ADA members on how likely I think it is that they'll be the PM transfer
Kunikida is far too driven by his ideals, morals and ideas of righteousness. He certainly doesn't have the most powerful ability in terms of combat and would therefore not be the Port Mafia's first pick either way. If they were to pick him he would probably refuse to collaborate and he'd cause more harm than good to the organisation.
Fukuzawa's low on the list for many of the same reasons as Kunikida.
But I think he'd be more favoured than Kunikida by Mori, because of his combat capabilities and past moral ambiguity. As the president of the agency he's central to their dynamic too and it would shake the agency up, even if Kunikida were to replace him.
Kenji's one of the strongest fighters in the ADA. But his ability is somewhat unpredictable and Kenji's very naive, which isn't a good thing to be in the criminal underworld. Mori is also probably the least familiar with him out of all the members of the ADA, so I can't really pinpoint a motivation he'd have for choosing Kenji.
Tanizaki's ability is very useful and would be perfect for crime. We also know very little about Tanizaki's past and backstory, so him becoming more in central in the next couple of arcs would be logical as he's the only member of the ADA that hasn't really been given this kind of attention.
But so far, it's unclear how central the transfer is going to be. For all we know, Tanizaki transferring could lead to less plot relevance for him.
Kyouka has already been in the Mafia, and is an experienced murderer. She also seems more prone to going back to her criminal ways than the other members when protecting the people she loves.
What stops me from putting her higher up on the list is that she fought long and hard to quit the Port Mafia, and would probably continue to do so if she came back. Kouyou and Akutagawa are both also content with her place in the light, and probably wouldn't vouch for her return.
I've seen a lot of people theorise that she'll be the transfer, which is seemingly impossible as her not transferring is the one condition of Fukuzawa and Mori's agreement.
However, the only person who knows about this condition is Fukuzawa. If something is to happen to him, which Mori may be relying on, then she'll have no choice to comply. I think that she's almost guaranteed to get picked if Fukuzawa dies, but I find that unlikely as of now
Her ability is extremely powerful in terms of healing, and would be of great use to the Port Mafia. If she were to quit the Armed Detective Agency then the stakes would be a lot higher. In Yosano's own words; almost dead is the same as completely fine in the Armed Detective Agency.
She'd probably be reluctant though, and forcing her to join the PM at all would be tricky since she'd rather die than use her ability the way she used it in the war. That's why I rank Ranpo above her.
Ranpo's the pillar that upholds the agency. It was started because of him and he's the person who keeps them in business.
We're also unsure of what Mori's motivation for the transfer is. If it's to hurt the agency, then Ranpo would be the best way to do so.
Ranpo is also one of, if not the smartest character in Bungou Stray dogs. He would make an incredible strategist for the Port Mafia, and holds a high amount of power within Yokahoma's law enforcement. Ranpo could probably make innocent people take the blame for crimes committed by the Port Mafia. But he may be too smart for Mori, which would lessen his chance of getting picked.
Atsushi's the main character of Bungou Stray dogs, which makes him a likely candidate for the transfer. He's also shown to be very self-sacrificial, and would probably offer to go instead of someone else. I could see him for an instance try to give himself up for the sake of Kyouka or Dazai.
Additionally, he's one half of the newest generation of Double Black. Him and Akutagawa are often shown as parallels, and giving their relationship more depth and screentime would be a logical step for the show. He's also one of, if not the most powerful fighter in the ADA and his ability is said to be The Book's guidepost.
If the Port Mafia's after the book then Atsushi is the best choice they can make.
The only way I can honestly see Dazai not transferring to the Port Mafia is if the setup for him doing so is a red herring.
First and foremost, Dazai's blood is "Mafia black" as Higuchi put it. He has a long history in the Port Mafia, and used to be central in it.
When Dazai was fifteen, Mori predicted that he'd take over the throne in seven years. Now he's twenty-two.
Mori's shown to be an intelligent and manipulative man, and it's not impossible for him to have deliberately killed Oda Sakonosuke knowing that it would lead to Dazai going to the light side. Whilst Dazai was certainly useful, he wasn't a good mentor or leader, as shown with the abuse he made Akutagawa endure. Him going over to the light side made him more compassionate towards his mentees, as shown with Atsushi.
There's also been a very clear development with him in the last couple of seasons. Dazai's crimes were leaked, and he may not be able to return to a normal life even if the agency prove their innocence. Even if his old crimes are erased again, he has also committed new ones, like jailbreak. He's also repeatedly shown with his bangs covering his right eye, which parallels the bandages he wore "in the dark".
We see several characters forgetting to count him as a part of the Armed Detective Agency. They may have forgotten it, but it's more likely that they've realised that Dazai's going to be the transfer or that it's foreshadowing.
And whilst he was central to the plot, Dazai was separated from the rest of the Agency in the majority of season five, and could only communicate with Ango. This may have been a demonstration of the Agency's capabilities without him, and they were shown to manage the crisis on their own.
Everyone has their own role in the agency, except for Dazai and Ranpo who share the role of the "brain". If Dazai were removed, then Ranpo could probably cover his bases but Dazai couldn't cover Ranpo's bases.
There's also his partnership with Chuuya. It was focused on a lot during the Meursault arc, and is the focus of a lot of light novels. It would make sense to have Chuuya be a more central character by having him team up with Dazai, the shows secondary main character. Chuuya's character development is clearly not near finished, and reuniting with Dazai would accelerate it greatly.
Lastly, Dazai's a genius and a part of Double Black. His return would not only bring back the Port Mafia's infamous weapon of Corruption, but also their infamous strategist and Demon Prodigy.
These are all of the actual clues, so this last part is just me going off about the Dazai-is-the-book theory and why I think it fits in with this:
Mori knows more about Dazai than the other characters, and he's also the leader of the only organisation not shown to be after The Book. Dazai's life prior to him joining the Port Mafia is a mystery, and might be very central to the plot.
The book is said to be sealed, and Dazai might very much be the seal. If he was created by The Book in order to seal it then that would explain his suicidal tendencies. He's a projection of the page on which the seal was written's wishes, and if the book wants to be destroyed then he wants to destroy it. Alternatively, the seal was forced upon the book, and can only be broken by his death.
If he wasn't created to be the seal, but rather was given the role by someone/thing else then he could be suicidal because:
a) he wants the seal to break and the book to return
b) he wants the book to be destroyed
If this is the case, then Mori would have good reason to want him back into the Port Mafia. It's not unlikely for Dazai to "replace" him upon his return, which Mori is well-aware of.
Isn't that a bit weird? Unless, Mori has more important motivations than the preservation of his own life. Like for an instance getting a hold of the book, or a chance to destroy it.
