HOMG I GOT MY HAT LADY!
. . . I think. ^^;
I mean, the resemblance is uncanny, don't you think?
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I admit I don't think that Okiya is Bourbon, or that ScarAkai is Akai anymore, now that Akai's sister (most likely, based on her eyes and name) is here. I think my new theory is that Sera Masumi is both Bourbon and ScarAkai, and that Okiya is a new character. As for who Akai is, I have no idea.
I think that the glasses guy and hat lady are Okiya and Sera, respectively. I know, the glasses guy and hat lady appeared in Ch. 419 and Sera appeared in Ch. 768, but I'm not saying that Aoyama plans hundreds of chapters ahead - rather, that Aoyama puts hundreds of fillers between plot. So why do I think that Okiya is a new character and not Akai? Because the end of Ch. 419 implies that the glasses guy and Akai are two different people:
Spoiler:
I think that Bourbon is an ally, since Rena said s/he started moving right after Akai was rumored to be dead. I think the "Only I get to kill Akai" line served to protect Akai more than harm him, since the line scares other members away from killing Akai themselves, and if Bourbon didn't have an intention to harm/kill Akai then Akai was more or less safe within the BO. I had trouble thinking that ScarAkai would be part of the BO, since disguising as Akai wouldn't accomplish anything - disguising as Akai wouldn't help getting intelligence on the FBI, since the FBI would regard ScarAkai as an obvious trap, and the BO would freak out and might accidentally kill ScarAkai - but it makes sense if there was an ally within the BO who wanted to check if Akai is dead or not. Okiya also says that the "pack of wolves . . . lost their easy prey" (Ch. 704) when ScarAkai escaped, and if wolves = BO and ScarAkai = prey, then ScarAkai would be someone the BO should like dead. If Sera really is the hat lady (who seems to have worked with Akai and the glasses dude [who I think is Okiya]) and is Akai's sister, then she's an ideal candidate to be Akai's ally (aka Bourbon) and Okiya's ally (aka ScarAkai). Plus, there'll be reasons for her to try to find out if Akai is truly dead or not, hence her disguise as ScarAkai, probably with Vermouth's aid.
Which brings me to think that Vermouth could also be an ally. Vermouth refers to the BO not only as wolves, but werewolves - maybe this is Akai, Okiya, and Sera's code for the BO or something? She does seem to want to bring down the BO in her weird way.
EDIT:
I'd also like to add something . . . Haibara says at the end of File 304 that Gin is left handed, yet File 242 shows Gin shooting a gun with his right hand. Huh. Nvm! Not sure why I thought Gin was using his right hand when he was clearly using his left hand . . .
EDIT: Another potential glasses dude appeared! Although, Amuro, Okiya, and Sera's vehicles are different from the one the glasses dude was riding. I did think that the glasses dude's car looked like Detective Satou's, and Amuro's car is the white version of Satou's, but the driver's seat is on the right, not left side. Okiya's car is completely different. I guess this means that the glasses dude was James, and that's why James recognized Sera? If this is true, why is James trying to hide Sera?
EDIT: Hmm, I just found out that James' and glasses dudes' cars are pretty similar:
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