If I’m going to stick with what I’ve said in the last post. Then we already have two cases related to Kumiko’s past solved by the 10th episode. The first case was Kumiko felt bad about Reina, though she doesn’t think she was at the wrong side, she keep dragging the fact that she is troubled with it. Turns out it was just her thinking too much, and on the other hand, she actually got Reina attracted to her.
The second case was revealed just now, Kumiko has this episode where she being scapegoated by her senior. That’s why she feels troubled now since Natsuki doesn’t pass the audition. She totally thought Natsuki will spit on her.
Again this is just Kumiko worrying too much. Natsuki invited her for a talk and laughing it off. She knew Kumiko troubled with the audition result, but Natsuki has just playing eupho for 1 year and she knows it’s obvious that she wont make it. She rather thankful for Kumiko, that she can improve her playing and enjoying it a bit better.
Now here be spoilers