In a flashback in volume 7, it was revealed that like Kotori, she was originally a human prior to becoming a Spirit. She wasn't good at anything but singing, but she could sing better than everyone else around her, and hence had dreamed of performing on the big stage from a young age. Her dream came true at the age of fifteen when she debuted under the stage name Tsukino Yoimachi (宵待 月乃 Yoimachi Tsukino?), where she had the time of her life, being loved and adored by her fans, of which over 90% were male. A year after she debuted, she refused to sleep with a TV producer, after which false scandals about her began to appear. She quickly lost favor with her agency and her fans, leaving her devastated. She tried to reconnect with her fans with her singing, but suffered psychogenic aphonia on stage, resulting in her losing her voice, her one asset. This led her to contemplate suicide until Phantom approached her and gave her her current Spirit powers. Due to this incident, she stopped trusting everyone, hating on males and seeing females as her slaves and puppets. However after seeing Shido put his life on the line to rescue Tohka from DEM's clutches, and later keep his promise to do so for her as well, by saving her when she gets attacked by a frenzied Tohka after running out of Spirit mana and losing her voice, rendering her defenseless, she falls in love with him, deliberately initiates the kiss to allow him to seal her powers, and even calls him "darling", trusting him to keep his promise to continue to be her fan even if everyone else turns against her. She loves Shido to the point of declaring him to be her boyfriend around others.
Her Angel is Gabriel, which takes the form of an organ complete with speakers, through which she can transmit and strongly amplify her voice, and by extension her sound-based powers, of which she has demonstrated three so far: March, which enhances the listeners' physical strength, Rondo, which generates sound pressure in the form of a wall and is her primary form of defense and attack, and Solo, which brainwashes her listeners to cause them to be devoted to her, but can be blocked out by a pair of earplugs. A devoted follower will refer to Miku as Onee-sama (Formal Japanese for big sister) and think or do things they normally wouldn't do, even if unasked, to help her out no matter how insane the action. Such as what Kotori and crew were about to do as punishment to all the people, especially Shidou, who had hurt Miku before being interrupted. Her AST codename is Diva.
Source from Wikipeida