Here is some cbox transcription for reference.
Chek: Ugh, I really don't want to do anything more about the child issue until more clues appear, but it looks like I have to ask a question for the sake of completeness. What are the pronouns, speech types (feminine, masculine, ambiguously polite) being used? Subjectwise, Masumi directs a question towards the child at one point, and the child refers to itself a few times.
Zenthisoror: She uses watashi, and she speaks in a very unchildlike, cool adult-like way, a bit like Haibara, but she's not as girly as Haibara.
Chek: When Masumi asks the child about its opinion of Conan, did Masumi's question contain a gendered pronoun? Basically, I'm trying to get a sense of whether Gosho is blocking Masumi from addressing the child in a way that would reveal its gender. Since they are alone, I can assume that they are likely to be truthful to how they normally would address one another.
User 4869: Haibara is girly? sorry off topic.
Zenthisoror: In the Japanese, well, Haibara's pretty feminine.
@Chek: Hmm, I think considering that Lady Oscar tells Sera to refer to her as a kind of 'little sister' she's probably a girl?
Chek: @Zenthi, I'm concerned that the child is a reverse Sera, a feminine boy, who is using their ambiguous appearance to disguise from whoever.
User 4869: a little related http://forums.dctp.ws/viewtopic.php?f=5&t=11727&start=45#p791042
6 Nov 13, 08:50
Chek: But anyway, besides the question above about how Masumi addressed the child, a user at DCW asked about a -nasai (Black Demon corrected spelling) motherly ending. I can't elaborate on the context...
Zenthisoror: @Chek: A reverse Sera would be interesting. To be fair his/ her speech pattern is more boyish than girlish.
Oh, kotaenasai right? I wouldn't say that's motherly - it's a semi-formal order.
Chek: Maybe that's it. Honestly I am more concerned with how Masumi addressing the child in her question about what the kid thinks of Conan. I want to know if Gosho is dodging gendered pronouns, implying a trap. Well, a male who uses watashi probably would be formal-ish if kiddo is a male and not a female.
Zenthisoror: I guess because in Japanese you don't really need to use pronouns to speak and sticking them in just makes the speech kind of unnatural...let me have a look at what Sera says then... She talks to the kid like an equal? No noticeable sense of respect or hierarchy. This could simply be because of Sera's personality, but she seems familiar with the kid and the kid is familiar around Sera. Having said that, the kid comes across smarter and cooler than Sera and, of the two, more like the person pulling the strings.
Black Demon: If Gosho is trying to hide her true gender then I doubt that we can find anything conclusive for now.
Zenthisoror: Best bet at the moment, I'd say a shrunken woman familiar with Sera, so probably her mum. I am ecstatic. (sarcasm drips off me like a melting ice lolly) @Chek: No signs really. If anything, he's either leading us on to think she's a girl, emphasising she's a girl or seriously tricking his editor into thinking she's a girl.