Bungou Stray Dogs
I've seen this trope before (maybe a lot), but what if Chuuya defected the Port Mafia along with Dazai?
He would definitely make sure Dazai took care of himself, and would manhandle Dazai into anything if it worked in their favor. Also because he's still a loyal shit with a lot of sympathy and empathy and would want to help Dazai anyway even though he thinks the guy is an utter asshole.
When they join the Armed Detective Agency, Chuuya often is the responsible one out of the two of them, as usual, and Kunikida is often crying in joy at the fact that Chuuya actually does his paperwork and everything he is supposed to. They are often paired with Kunikida due to an odd number of members. Chuuya and Kunikida get along swimmingly and often despair about the torment they get from Dazai.
When Atsushi comes around, Chuuya takes one look at this poor fool who decided to trust in Dazai without realizing how irresponsible the man could be with certain duties, and feels pity. He can also tell this poor tiger is in desperate need of validation and affection. He tries to guide Atsushi in a way he did not with Akutagawa, a guilt that follows him around (because let's be real, Dazai treated Akutagawa horribly even though he's better now).
..............etc. etc. skipping a few arcs because I'm lazy—
They are revealed to be formerly known as Soukoku, the Port Mafia's greatest weapon and most powerful tool of all time, and their peers are shocked. Sure, they were former members of the Port Mafia, but Soukoku? Yeah, it's a shocker. Except Ranpo is the same as usual. He already knew, because he's an amazing detective.
Obviously they aren't happy to be working with Mori again (even though it's not under him this time) and Chuuya gets a little affected seeing Kouyou again after not seeing her for years.
......
......
......My idea falls flat here........
But idk I think I just like this trope a lot I just love seeing Soukoku together