The hairclips would indicate it being Hideyoshi. As far as the genderswap thing goes, I'm just going by the comments in post #664512 If there's evidence to the contrary, then feel free to change the tags.
He/she has a TRUE-FLAT chest, not a girl's usual flat chest, and the question is whether he/she has a manhood hidden under Yoshii's body. I think it's a normal Yaoi+Sex, no genderswap here.