Definitely not Kou. Kou would be looking for Mitsuba, in any case, and there was no way he knew that his brother remembered the other world too (or that Nene remembered), so separating her from the rest made no sense unless he was a fake luring Nene to not-Hanako
idk i feel something off about kou? is that the real him? or.. idk.. i just feel like that's not him ( ;∀;)