Alpha Chuuya -> Omega Chuuya X Alpha Dazai
There’s many theories on how I think Dazai bitched Chuuya but here’s one of them…
Starting off with a month/months of subtly scenting Chuuya. To get Chuuya's body used to smelling like another alpha and confuse his brain into believing he belongs to another alpha. Chuuya didn’t think much of Dazai being close to him during the weeks because Dazai is always latched onto him.
Then Dazai would leave his clothes around Chuuya’s apartment to scent the place for when he’s not there as well as have something Chuuya can use whenever the nesting instinct starts to come in. All the clothes are ones taken off after a mission, Chuuya thinks Dazai is just being plain annoying by leaving a mess of dirty clothes behind for Chuuya to pick up.
A few weeks after this and Chuuya’s scent starts to change, it's a very subtle sweeter smell that you’d only notice if you were really close to him prior.
An alphas' instinct to lead and dominate is a hard behavior to get rid of, but that’s not a hard task for Dazai. Dazai is always bossing Chuuya around, from missions to stupid obscure tasks. Chuuya is nearly always on his feet for Dazai's demands.
When Chuuya’s next rut was coming around, Dazai offered to help to which Chuuya immediately shuts down “How would another Alpha ever help me?”
Dazai insists that him being there would make things easier and that alphas knots really work wonders, even to other alphas “Alpha knots have healing properties that help reduce stress. Alphas used to knot other Alphas all the time in the military during war, it really helped them fight their battles. You should seriously pick up a history book everyone knows that”
Chuuya knew he was lying but felt that there was no point in arguing with him. So he consented to having Dazai share a rut with him.
During the rut I’d imagine Dazai whispering things like “perfect omega” or just anything you’d only typically say to an omega in heat to really trick Chuuya’s brain into believing he’s an omega. Chuuya would be too fucked out of his mind high on his rut to understand nor hear what Dazai is saying.
Right as Dazai's knot pops he pinches Chuuya's mating gland, imitating a mating bite. From the weeks of scenting to dominating Chuuya around, Dazai's knot finally seals the deal causing Chuuya’s scent to change as well as leak slick.
But I like the idea of Dazai unintentionally bitching Chuuya, making them both surprised in the end when Chuuya just suddenly turns into one leading to Dazai's stupid comments of “see you were always meant to be my dog.”
I feel that the process would be exactly the same except instead of a shared rut it’s just months of dominating and scenting the other, causing Chuuya’s brain to see Dazai as his Alpha.
His body would see no purpose being an Alpha, having the biological need to provide children for their mate and seeing how he’s not going to get his mate pregnant. His body would just evolve to where he can.
Normally bitching is a long process of constant knotting. But if the body recognizes the other as “mate” the process is much faster and less sexual