Aya has always looked after Suiren since they were children. The boys would often pick on Suiren because they liked her and Aya would always stand up for her. She continues to take care of her to this day and is Suiren's closest friend. She also makes fast-friends with Yuri at the start of the story.
Aya has short, straight black hair with short bangs swept to the right side of her face. She is usually shown with dull, uninterested eyes, especially when speaking to Takaya Ryousuke, but becomes serious when it comes to Suiren's safety and/or wellbeing, emotional or otherwise. In reality, her eyes are very big and similar in shape to Suiren's, although her eyelashes are much shorter.
She is seen primarily in her school uniform.
Aya has a tomboyish personality, which likely developed after years of sticking up for Suiren. She doesn't appear to have a problem with this in the least. She does appear to feel lonely when Suiren and Kawasumi begin dating, feeling left out.
Usually carefree, or just plain disinterested, Aya only truly shows any interest if it has to do with Suiren. She is very protective of her because she understands how Suiren has been treated since she was young, due to her looks.
She seems to be much more mature than the other characters in the manga's cast and seems to be the least affected/invested emotionally in Kawasumi and Suiren's relationship.