You can't really tell with Mokou, but I'm pretty sure Keine's been genderswapped. Artist mentions that in pixiv.

I´ve learned the hard way that flat chest equals male until stated otherwise. Thank you Lord for the tag system.

Then again, there ARE genderswapped Mokous out there with the ribbons and all, so...

if it werent for the tags i never would have known it was a genderswap

I would've thought the obvious lack of tits on Keine would have been enough.

Whimsii said:
I would've thought the obvious lack of tits on Keine would have been enough.

Yeah, but without the 2boys tag you'd never know with Mokou. She's drawn with a less male-looking face here than Keine is, and flat-chested Mokou is far more common than flat-chested Keine.