Idk if this is ever talked about in the fandom but I think some really interesting parallels between Atsushi and Akutagawa are actually the people who took them in- the orphanage headmaster and Dazai respectively- and how they were pretty damn similar (at least at the time)
First of all, both Atsushi and Akutagawa both had little to no connection with their parents. They’re never mentioned because neither of them really knew them in the first place.
And then, both the headmaster and Dazai “saved” them from their shitty living situations (the word “saved” being in quotes because Atsushi and Akutagawa were simply moved from one shitty situation to another). The headmaster said things like “Compared to what your parents did, this hardly even counts as abuse,” maybe trying to justify his actions, and Dazai promised to give Akutagawa a reason to live, which made Akutagawa’s mental state pretty much dependent on Dazai.
Dazai physically and mentally abused the hell out of Akutagawa, as did the headmaster to Atsushi, while both simultaneously taking up this role of “caretaker” for them. The one main difference between them was that Atsushi actively hated the headmaster. And then there’s Akutagawa, who, as we all know, practically revered Dazai and did everything to get his acknowledgment, his approval.
And an impact I think these different outlooks had on the two boys was how they each treated Kyouka.
Atsushi knew how awful abuse was and viewed the way he was treated in a negative light, so he wanted to save Kyouka from the abuse she was facing. But with Akutagawa, he viewed the way he was treated in a positive light (for the most part, anyway), and so of course he’s going to try to treat Kyouka the way Dazai treated him. Most importantly, Akutagawa tried to give Kyouka a reason to live. Moreover, he thought her reason to live was simply to be an assassin as her ability was perfect for bloodshed, which is what he thought was his own reason to live given to him by Dazai (even if Dazai had tried to tell him it’s stupid to only use his ability offensively).
Something I also think about is how Dazai joined the mafia for his own reason to live, promised one to Akutagawa which became why he joined the mafia, and then Akutagawa tried to push that trend onto Kyouka
While Dazai gave Akutagawa a reason to live, the headmaster made Atsushi want to prove he’s worthy of living. Obviously, the Guild arc points out the rift this creates between Atsushi and Akutagawa and their motivations (even if this was from before Akutagawa’s past was shown).
Now, back to the actual topic at hand after going off on a sort of side tangent, there’s one more thing that makes the headmaster and PM Dazai parallels is their own backgrounds and how they affect how they treat Atsushi and Akutagawa.
Now, if I’m being completely honest, I don’t feel like rereading the chapter that described the headmaster’s past nor do I have the energy right now to look at his wiki (it is currently 3:22 AM as of writing this sentence), so I’m just gonna be going off my memory. BUT.
If I remember correctly, the headmaster was raised in an orphanage himself, and one that was in WAY worse conditions than the one he ran. Imagine the abuse the kids at Atsushi’s orphanage felt but worse. Then there’s Dazai, who was taken in by Mori of all people after a failed suicide tempt as a young teenager. Mori abused Dazai (more mentally than physically), and kinda… yknow, corrupted him.
So, both the orphanage headmaster and Dazai came from places where they were victims of the own abuse they committed.