Aya is a young girl, who is almost eleven years old. Her hair is black, and reaches down to her waist. It is styled in a clean manner with the bangs cut evenly across her forehead, just above her eyes. Her normal outfit consists of a blue, puff sleeved ankle-length dress, with a white apron worn over it, and tied in a bow in the back. As accessories she wears a necklace with a gold pendant, and a big pink bow on the back of her head.
During flashbacks, Aya is shown wearing a simple blue dress with a white dress shirt beneath it. At this age, her hair is shorter, and only reaches to her shoulder blades. It is also styled differently, being kept in twintails by two light blue, almost white bows.
When Aya is turned into a doll in the bad ending she is seen wearing a large white bow in her hair, her usual gold pendant and a floor length red ruffled dress with a bow on the left side of the chest. She has a sad, empty expression on her face and her usual dark blue eyes are grey.
In the true ending she is seen with her hair cut just above her shoulders and no longer wears the bow.
Aya is a good natured girl that truly loves her family. Despite of her father's morbid activities and affair she continually strives to think positively and try to live a normal life. Her father, however, won't allow Aya to go outside and mingle with the other kids in fear of physical danger, so her only companion in the house is her pet rabbit, Snowball. Even with the lack of a social life Aya maintains a cheerful attitude. It is noteworthy that despite witnessing things that are too horrific even for most adults or could drive one to insanity Aya is still able to keep a level head at a very tender age.
Her love for her parents is one of the driving forces in the game. It is shown in flashbacks that she is raised normally by her parents wholeheartedly, cementing her belief to love family to the end. Lack of outside life didn't hinder her maturity because of her parents' attention and constant care. This fact is what causes Aya to believe that her parents are genuinely good. Her devotion to both of her parents is what encouraged her to face tasks that are seemingly impossible for a girl her age to even consider undertaking.
She would try everything in her power to save a loved one; even potential enemies. When the curse started, tormented spirits began to reanimate to relive their desperate last moments. Whenever faced by these spirits, Aya would help them to gain freedom at the cost of her safety. One incident that showed Aya's compassion was when their maid, Maria, was betrayed and injured by her deranged father. Despite being hunted by the very same person, she mended her wounds and tried to help her. She has an uncanny talent to mend wounds much like Maria.
In the true ending, though, Aya's real personality was shown. It was implied that Aya might have turned out to be what her father was when she grew up; a sociopathic murderer. The red book her father had been reading was shown in her possession, having picked it up after leaving their burning home. Operating a small clinic in the middle of a forest, she shows goodwill to 'patients' to lure them unexpectedly to be experimented upon.
This strange characteristic can be sensed during the game by apt players:
- When looking in the drawers in her room, dead animals can be seen hidden within, in parallel to another story in the game where a kid became a murderer by killing small animals first and then killed his mother. In the Taxidermy room, there are multiple clones of Snowball; one has a cut in its leg and another has its belly torn. It can be assumed that her father had created this many due to Aya's mistreatment of her pet.
- There's a scene where Aya is strangely playing with a small chainsaw in their backyard, to her father's surprise. It could be assumed that Aya was, in fact, curious as to how her father does his experiments or she could have used the tool to kill small animals. It can be assumed that the 'original' Snowball was injured due to her using a chainsaw.
- Strangely, Aya is completely unaffected by screams and pleas for help. In the beginning of the game, Aya heard a terrifying plea for help from her father's basement and ignored it completely. The lack of sympathy for other people, except for her loved ones, may be due to her lack of a social life outside their home.
- The bookshelves in Aya's room it contain books that are darker in nature for a young girl to read. The Dark Quartet features morbid themes about death and torture, and Horus the Trader and the Red-Eyed Stranger allude to the 'salesman' named Ogre.
- After playing a second playthrough there are notes scattered in the game that weren't in the first playthrough. The notes depict her father's observation as Aya grows up. It is stated that her father had noticed Aya is starting to have 'curiosity' about anatomy and death similar to his, mimicking exactly what her father had done in his childhood.
- There is a note that her mother wrote that suggests slight insanity on her part too. It could be noticed in the first playthrough that her mother told her eerie stories before going to sleep.
- Aya is completely unaffected by the rooms of the trials of murder, in fact, her attitude is almost understanding. For example, after getting attacked on a couple of cases, she simply leaves/runs out of the room and says nothing afterwards.
- In the 'true ending', Aya encounters a red book before leaving, a red book that her father had. It is assumed that she had read the book, and drove herself mad. The book had 'gross pictures', so Aya refused to read it as a kid, but later on, she almost certainly read it. There is a rumor that the book may have consisted of directions to make people into dolls, or, as a few people have said, the title is possibly "The New Text of Anatomy."
- In 'Misao', Aya`s clone (Which was shown in the extra cutscene of Mad Father) was rumored to be the same Ms. Library due to some theories Ms. Library said. Having a mad scientist for a father, I will never be able to eat hamburgers again and also when you walk into The Library (in Misao) the music from Mad Father starts to play.