As a Supporting Actress, She Just Wants to Show Off, but the System Won't Let Her

The social beast disguises herself as a vicious female supporting character, and perfunctorily follows the plot in order to collect her pension. Unexpectedly, every time she commits evil deeds, she becomes a divine aid to the protagonists. In the end, she, a bug who just wants to be laid to rest, becomes the only variable that tears apart the established destiny and saves everyone.