Been on an a/b/o dive recently (more like I have an idea that won't leave) and I would like to say that while I enjoy alpha!Chuuya and love omega!Chuuya, the bsd fandom is severly lacking beta!Chuuya.
While yes, he's one of the strongest characters in the manga, and his whole being/personality could fit that of a stereotypical alpha, and yes, we could also put him as an omega, for 1. the angst and 2. the breaking of stereotypes in omegaverse (hello patheticzai), it would be also good if he was a beta. Mainly for shits and giggles, but also because the lab wanted someone who would be strong and a good weapon. Alphas and omegas both have their cycles, therefore they have one week/few days a month/year (depends on which verse is this) full of no brain, only their inner dynamic talking. Meaning they are vulnerable. Now it's terrible, but if I, or anyone really, wanted to build some weapon, that is supposed to win me a war, I would make sure that the weapon cannot be compromised anymore then stricly neccessary. So in a/b/o setting it would be most logical to go for a beta male (is minimaly effected by the cycles and smell, but also pathriarchy/sexism).
Now, to make things even more interesting, no one really realises that Chuuya is a beta, they always assume he's *whatever dynamic is Dazai's*. Like at best Mori and Hirotsu know, and the sheep, probably (maybe not even them, they just assume he hasn't presented yet, bc the strongest ones are surelly alphas) bc they met him before he frequently started hanging out with Dazai.
Dazai ofc has a perfect control over his scent, so most don't actualy know his dynamic, therefore don't realize Chuuya's walking around smelling like Dazai's property/possession/mate/whatever just Dazai's.
So imagine, sometime after Dazai leaves the mafia, people notice that Chuuyas scent is gone! There are theories, that he got rid of his scent glands to prove he won't ever betray the port, like his partner, which severs him to his second dynamic (basically handicaps him). Or that his long term romantic partner left him, around the same time as the demon prodigy, adding salt to the iwound (if he smelt like his romantic partner everyday, they must have been possessive, why did they break up?).
Timeskip four years, some members meet Dazai, who, while not open about his scent all that much, still allows himself to be scented and to scent his fam— I mean, the ADA in return.
Even more theories, the gossip mil in port mafia is thriving, even Fyodor is convinced that Chuuya eather dated someone from the ADA or Dazai has the same secret lover.
They once saw Chuuya smirk at Kunikida, and Kunikida to turn away from it. Nobody knows what they were talking about, but clearly Chuuya was taunting his ex, who so rudelly left him at the same time as his work partner!
Or maybe said ex is Ranpo, because he clearly WANTED to be stuck in a book with executive Nakahara. They could have just send him a text or something that Poe wrote at the time, surely.
It was debated for a little while if it wasn't Yosano, but somehow the gaydar of most is not wrong, despite every other conclusion.
Cue skk coming back from Mersault. And it becomes clear.
— gossip mafia members, who wanted the second theory to be true, at some point.
Chuuya and Dazai for sure dated Fyodor. To keep an eye on him.
Mori and Hirotsu are watching (dissapointed and amused respectively).
Cut to Atsushi (possibly even Kunikida) in the background - "YOU F*CKED A PORT MAFIA EXECUTIVE, WHILE WE WERE ALL DYING HERE!!!???? WTF DAZAI!?"
(The only other people, who knew about Chuuya being a beta, were Albatross (idk if the rest of the Flags too) and Arthur Rimbaud. One because the scent washed away after a swim back from a mission, the other because he also met Chuuya when he was with the Sheep, Verlaine assumed he later presented.)
(On the other hand, only Oda and Mori knew that Chuuya is walking around smelling like Dazai)
(I know i can twist it to kunichuuzai, but that's not really what I want to think about rn)
(The PM hated the ADA for the break up story)