No offense but if she turns out to be a fujoshi I'm personally disqualifing her as a heroine, I mean I got enough of that nonsense when watching, Noucome(anime) from Chocolat
Everybody, you're focusing too much on the obvious. Page 17, "Girl, huh...". Maybe she isn't. Idk why, some things just started falling into place this chapter, false positive or not.
So,then,what's left for the sister ?
She get in her oniichan bed,totally naked,lick him,and record it?
Or she is a super duper famous siscom doujinist that,of course,use her brother and she as characters?
I'm also for the crossdresser / trap thing. At the beginning MC explains us how she is "just the average girl" with shorten skirt etc. and her "Huh, girl ..." is way too suspicious.
@Australis thats what I think, every time theyve shown her staring and blushing was when the two dudes were together and she also doesnt want him to be with any girls