Just a random thought that occurred to me but am I the only one who sees a huge similarity between Mikoshiba and Dazai? Their vibe is similar, their antics are so random yet you'd be surprised at how reliable they both are, and although Yakumo and Atsushi are VERY different, the interactions between Yakumo and Mikoshiba in the stage play made me think: Oh they're just like Atsushi and Dazai
I never really thought about it, but you do have a point with Mikoshiba and Dazai's similarities...
In the context of the Initial File stage plays though, you might felt Yakumo and Mikoshiba's interactions more comparable to Atsushi and Dazai as I feel they've exaggerated the interactions quite a bit, it being a kageki and all. As I recall (I think it was from an interview or article?), Kaminaga-sensei pretty much gave the stage director Miura Kaori full creative liberty on the script and direction of the adaptation.