Hitomi Karuko

She is an author whose killing good is a piano called "Pianissimo of Ecstatic Symphony" that kills people after listening to the final note, she is a talented pianist and runs an inconspicuous bar called "Velvet" around the street alleyways, where Iwai's father frequents. She is blind and relies on her "Instead" Houichi to help manage bar, tune her piano and depose of the garbage which includes victims.

(Source: Otaku-streamers forum)