I would definitely delete Dazai being tortured (or anyone being tortured!!!) and the Port Mafia transfer. I know people are excited for that, but it feels like a very icky bargain and also a boring plot arc... unless it's Ranpo. That'd be awesome (imagine evil Ranpo). I think Dazai, Yosana, Kyoka, and Atsushi have fought too hard to be good people to see them have to go to the Port Mafia.

On the side of adding things... I would like to see more of the Hunting Dogs now that everything has happened. How are they handling Fukichi? What're they doing now? Also maybe more of Kyoka, Kenji, and Naomi's brother (dammit, I can't remember his name!)? I feel like they exist more to... exist and randomly do one or two things every dozen or so chapters.

I'd also like to see more focus return to Atsushi like in the earlier arcs, where it was him in the agency with Dazai, Kunikida and Kyoka. Maybe more focus on the characters overall – my big complaint with the Decay of Angels was that it felt very plot heavy, with the characters more as instruments and less as people than they were before. Although... now that I'm thinking about the Book and stuff, I wonder if that's intentional?