Serika Kouzuki begins as a shy and insecure individual. Her development stems from intense frustration and envy toward classmate Shion Asahina, whose violin playing exhibits far greater refinement. This turmoil drives her to seek private lessons from teacher Akio Yashiro.

Yashiro manipulates her musical progress, imposing the condition that improvement requires her to be sexually aroused. Under this coercive tutelage, Serika's relationship with Yashiro transforms beyond student and teacher; she becomes his accomplice. Her personality shifts significantly, marked by growing enjoyment in tormenting and humiliating classmates.

Serika's narrative centers on an object called the "Demon Violin." Its power presents pivotal choices: subjugating others, overcoming its dark temptations for a positive resolution, or succumbing entirely as a passive observer to degrading acts. Serika's specific story trajectory—whether facing humiliation, descending into corruption, or finding redemption—is shaped by narrative decisions within her source material.