First appeared in Transparent Answer. A cheerful girl who was Shintaro's classmate. During the summer of her first year of high school, she made contact with Shintaro, who had a tendency to keep a distance, but who soon relented to her advances and genuinely enjoyed her company. From then on the two became close friends. Shintaro catches her crying one day, but is at a loss at what to do and leaves. The next day it is revealed that she had commited suicide for some unknown reason. (Source: Vocaloid Wikia)

Spoiler

Jin's eleventh song, Ayano's Happiness Theory revealed that she is the original founder of Mekakushi Dan (labelled as member no.0) The other three members, Kano, Kido and Seto were adopted by Ayano's mom into the Tateyama household at a young age. Being the big sister, Ayano tried to get along with the three children using many means. Then she decided to make a secret group, and even gave them hoods. When they were teenagers, Ayano's mom passed away and from then on, things went haywire. Her father was scheming to experiment on two of Ayano's school friends, Takane and Haruka. It is then revealed that one can obtain red eyes when exposed to a near-death experience. Believing that by obtaining red eyes she would possess the power to save her friends, she 'committed suicide'.