Yuri's reason in joining Gorgom is understandable. I mean, rich people don't care about the music, they only care about the glory it made to their family! Yuri just wanted to spread good music and not to be cheated by rich people! But that is not what is happening to Kotaro because her music hurts his ears because of the Cicada Mutant! Kotaro then transforms to Kamen Rider BLACK and fight the Cicada Mutant. Much to his surprise, his attacks affect Yuri's body. One thing I notice on her head is some special headband. By the looks of it, this affects her nervous system every time BLACK hits Cicada Mutant's body.
This is when the fight gets interesting, BLACK is thinking of ways on how to beat the Cicada Mutant. At first he tried throwing the violins, thinking that it connects to the Cicada Mutant. Though it failed at first, he then realized that the headbands are the ones that connect the Cicada Mutant's nervous system. I thought at first that BLACK will hit the headbands but much to my surprise, he hit Cicada's head that connects to the headbands! It's smart and did quite a damage that disabled the headbands before BLACK finished the Cicada Mutant with a Rider Kick!
At the end, Yuri came back to her sense and realized that even though she only has a single fan, he understands better music than most people. It's one great lesson that it is bad to force most people on what you like but to care people who like what you like.