So I bought the Definitive Edition and did not have access to Shin Hisako, Eagle or Kilgore, but suddenly this week I did! I have no idea why I now can play as those characters, since I haven’t done anything to get them as far as I’m aware. Is that a glitch or was there a way to access them that I didn’t know about?
Sounds like a glitch.
With the Definitive Edition, you should have access to all characters immediately.