When you complete the Tatsumaki route you will have two endings, and depending on the choices you made during the route, you will be able to unlock Tatsumaki's free use or Erin's free use.
Which one did you get?
In my experience there seems to be a sort of "relationship meter" and if you've clicked too many "wrong" dialog options you'll miss certain scenes regardless of routes chosen. This could not be the case but from I've seen you have to make sure the characters are "happy" to get certain scenes. In short, when you get option make a save and check them and gauge the reactions then make your dialog choices based on what the characters want to hear from the mc and how it might affect future events.