Her first name is Yoshiko (良子), but surname is not known. Phonon is a penname Yoshiko has used from her younger days. She thinks Phonon is the true name of her soul.
During the daytime, she's a student and Nanase's senior at the middle school they both attend. Phonon is a year older than Nanase. She and Nanase have known each other since grade school. Back then, they played magical girls outside. Phonon had very special original settings, and that later inspired her to write novels of her own.
Most of the time, she seems very wise-cracking and quick to look down on other people through a harsh and demeaning front. During the Hollow Night, she is forcing herself to act like dominatrix and this sometimes leads to awkward situations.
Phonon's normal hair color is black, but she dyes it to light green color.
Story
Episode: False Self, Real Self (偽りの身分、本当の自分)
Phonon starts to hear rumors about the Hollow Night about two months before the actual story takes place. Her curiosity leads her to the check if the rumors are real. On a abandoned back alley, she enters the Hollow Night and is bitten by a Void. Phonon is frightened by the happening and runs away as fast as she can.
After Phonon has recovered and returns to school, she is approached by Tsurugi from another school. Tsurugi thinks that Phonon has become one of the In-Birth. He explains that based on the rumors from that certain night and the fact that she had to take leave from school for a few days. In exchange for a weapon and further explanation about the In-Birth, Phonon joins into EFG with the condition that their alliance is only temporary.
Arcade Mode (アーケードモード)
She was a member of the student organization EFG for sometime and worked under Tsurugi. However, after she felt like she had paid back the debt she owed to the EFG, she decided to cut ties and act on her own.
She heads into the Hollow Night looking forward to enjoy herself in that paranormal world. From Gordeau she hears about a true dominatrix leading the organization, Amnesia, and starts to search for this person. When she comes face-to-face with Hilda, she steps into a landmine by calling Hilda an "old lady". The angered Hilda attacks Phonon with all her might.
After their battle, Nanase arrives to the scene looking for the boss of evil organization. Both of them recognize each other and Nanase is overjoying their reunion. Phonon is completely taken by surprise and decides she has to erase Nanase's memory of this encounter. Afterwards, Nanase is being considerate and acts like her memory was lost and speculates that she was assaulted by Kido Hyde. Phonon is happy with the situation as she leaves from the scene.
Abilities
Her weapon is a being called Muniel (ムニエル). Normally it takes a shape of a white snake, but when Phonon starts to battle its transforms into a whip. It was orignally a piece of Void which Tsurugi gave to her. After Phonon poured her EXS into it, the Void took a form of a whip.
Phonon's ability Baroque Noise (バロックノイズ) is the EXS of Swinging Sounds (振鳴のEXS). This ability lets her weapon to generate sound waves of varying levels, which has Phonon wear headphones to protect herself from its side-effects.
She wishes. For the paranormal ability from the deepest
spirit of hers. Along with the white follower. False shell at
present. The wish will be fulfilled when the time comes right
here. The sword speaks. The path to the bright future. She
fails. The sword exposes. The path from the cloudy past.
She overrides.
