Acatalepsy (アカタリプシー)/theories

Who is Akai Onna
Akkai Onna also known as lady in red, giant background girl in red seifuku, from special path with same girls but different sizes, so who is she can be? There is two theories about her. First one, judging by fact that her path lead to the train she can be friend of Naoto or even girlfriend, who escorted him on a train in a last way.