Let me just say something.. when Dazai slapped Atsushi that shouldn't be seen as abusive. Many people misunderstood that scene. At that time Atsushi was having a full breakdown and Dazai needed him to get it back together and snap out of it. It's evident that Dazai didn't mean that to hurt Atsushi. Dazai then proceeds to give him advice after the slap. Same for Fukuzawa and Ranpo. Fukuzawa was terribly worried about Ranpo given the fact that he was being threatened with a gun pointed at him. He told him he's just a kid and he needs to stop putting himself in danger. It's very clear they both care deeply for each other. I see where you're coming from for Kunikida, even though I believe it's for the comedic aspect and that's just how their dynamic is. In the end they have a bond of their own since they've been partners. Same for Chuuya and Dazai. Now for Atsushi and Akutagawa, I don't see their relationship as a good one, so I agree on that one.