It seems that Riina seems uneasy about something and it’s about being a rock idol.
From the looks of things, it’s quite obvious that Riina looks up to Natsuki as a role model. After all, she is more of a rock idol than herself. This is quite obvious since Natsuki seems to be knowledgeable about the rock genre while Riina on the other hand pretends that she knows something. In other words, Riina is a complete poser. Still, I have to admit that they make a cute couple regardless.
As for the main drama in this episode, it seems that Natsuki took the opportunity. She believed that her band could become popular. Knowing Mishiro’s logic, she wants full control of their band’s direction, including the music, costumes, etc. Obviously, this is not a good thing since the artist has absolutely no control of the creative process. In other words, the artist or singer can’t make any changes to her liking or contribute ideas since they are already being decided on.
What Mushiro is trying to do is something very taboo: selling out by trying to tailor their music to a mainstream audience. While it’s technically okay for a pop singer to sell out since most people won’t care, doing this to a rock band is a big no-no. The fans will think that you lost artistic integrity and will stop buying their music. In other words, commercializing or selling out a rock band is basically giving them a death sentence, which is something that Natsuki probably don’t want.
From the looks of it, Riina seems worried that she is not a rock idol enough. At the same time, Miku became anxious that her unit would break up since Riina might want to create a unit with Natsuki instead. After the accident that occurred during their live performance, which Natsuki attended, Riina insures to Miku that she won’t break up Asterisk and she stated that if you think its rock, it is rock. Yep, Riina’s poser mentality is strong, but it definitely left an impression on Natsuki as she listens to her heart. Natsuki literally gives Mishiro a middle finger and decides to join the Cinderella Ball to create her own style of rock.
In short, another attempt at selling out an idol falls on its face again as creative freedom lives on. It makes me wonder when Mishiro will give up considering that her efforts have been a complete failure so far. Probably until she gets fired.