|Occupation||Middle School Student|
|Relatives||Saruhiko Fushimi (second cousins)|
|Anime Debut||K Seven Stories|
|Manga Debut||K -Lost Small World-|
|Novel Debut||K -Lost Small World-|
|Japanese Voice||Yui Ogura|
Aya is a relatively short pale-skinned girl with straight medium-length brown hair that is styled in twin tails and held up by yellow bows with a straight fringe across her forehead separated in the middle with two thin strands of hair and light mauve eyes.
She wears a red blazer, white buttoned shirt tied by a red bow, and tannish-yellow skirt as part of her middle school uniform. Her backpack is a large, pink rabbit.
Like her cousin, she later wore similar style glasses in order to look more like him.
Despite her appearance, Aya has a sharp tongue and high self esteem. She is also shown to be very intelligent as she was able to decipher a code that showed the flight pattern of the strange blimp that floated around the city. She claims that the people who dislike her are more bothersome to her than she is to them. She talks with a certain 'tic', and in third person.
She also has a lot of pride as seen when Saruhiko Fushimi scared her and Misaki Yata with a ghost story and later telling them it was a joke; she cursed herself and said defeat would be a shame on her name. Because she is highly intelligent, Aya likes to be correct and stubbornly refuses to acknowledge any mistakes she may have made.
Because she felt Saruhiko hasn't been paying enough attention at her, she later grew to be more spiteful. She later made it her goal to gain the Green Aura from Jungle.
After Misaki Yata finds a letter stashed into his cubby hole he goes to talk to Saruhiko Fushimi about it and later runs into Aya, who was the one who placed the letter there. She cheerfully talks to the two boys (although Yata was visibly uneasy around her and hid behind Fushimi) and she proposed they go some place later. As Yata talks to her more, Aya claimed that she used to be in a group of girls who talked and dressed the same as she did, but left it later on.
When they all meet up, Aya explains to Yata through an app on how she found the flight pattern of the blimp that they were going to signal using a special light app on their phones. She turns to see if Fushimi was listening, and pouted when she noticed he wasn't paying attention to her.
As she met up with the boys and entered a building, she became startled by Fushimi's story about a woman jumping off the building, but her ghost did not remember dying; thus repeating the act of jumping to her death and muttering: "I can't die, I can't die". When she found out that it was a joke on his part, she was angered and claimed that a defeat in the Oogai family was a disgrace on her part. As they wait for the blimp, Aya angrily reveals her relationship with Fushimi as second cousins, although she felt no real closeness to him at all and said that Fushimi shouldn't have come with her and Yata who should be on the blimp. After she described Fushimi's mother's job, she laughed at Yata when he asked if Fushimi's father was a businessman. She said that the thought of Fushimi's father being the head of a company is hilarious.
She stops laughing after a while to take a call from her mother and gives the boys food to eat as they wait for the blimp to arrive. Some time passed and she asked Yata to act as a girl and begged him to do it because she didn't want to return home. When Yata had finished talking to her mother she tried hard to surpress her laughter throughout the phone call but laughed in the end saying his voice was perfect and her mother wouldn't be suspicious. Aaya becomes startled when she and Yata notice Fushimi laughing and even loosing the "tic" in her voice due to her shock.
Suddenly, the building they were in started to shake and they noticed that the blimp was elsewhere than where their destination was. Aya refused to believe she had made a mistake until Fushimi began to re-map their course. When she tried to proudly stick her chest out as Fushimi calculated the route, he ignored her leading to her frustration. Fushimi showed her the new route, totally different from hers, and she perversely refused to believe her mistake. Fushimi decoded the code and when Aya suggested it could be another hidden message, Fushimi shot down her ideas by saying it was just a prank.
- The name Aya means "Africa, flatter, fawn upon, corner, nook, recess" (阿) (a) and "question mark" (耶) (ya).
- Aya's surname Oogai means "big, great" (大) (o) and "shellfish" (貝) (kai/gai).
- In Lost Small World (Period 10), it is shown that Aya gets scared of ghost or horror stories.