Assuming they're the same person on one of the routes: What would be your explanation for the scene where Yamato is in bed with a sleeping Mio, watching Akemi live reply to his comment?
It's strongly implied that Mio knows of and treats Akemi as a separate entity later on. The account blocks and stalling while giving her response to Yamato's "Do you know Akemi?" question could go either way and be red herrings, but Mio doesn't strike me as an outright liar. Akemi doesn't seem like the type that would be motivated to go through all that effort to maintain a relationship like Mio has with Yamato. Mio adopting that role later, once she realizes Yamato is turned on by it, does make sense to me - but not her being Akemi from the start. That makes me think they're going to be different people on all routes...
I'm liking the separated-at-birth or grew-distant twin theory. Imagine conservative Mio, embarrassed by how her sister's actions might reflect on how her other conservative friends view (or fantasize about) herself, decides to move away to live independently where nobody knows she has a slutty twin. Then she gets a boyfriend with a cuck fetish and MiniTV happens. Split personality or secret double life Mio could be a hot and interesting story, but I imagine it will be challenging to tie that together with another route where they're separate entities. Definitely could be wrong, though!
