" Ueno and I kissed again yesterday . . . . "
Ayuko Oka is a classmate of Urabe and Tsubaki, Kouhei's girlfriend (he calls her Ayu) and Urabe's eventual intimate, Shouji Ai friend. She was first introduced when Tsubaki walked into an empty classroom to see her and Kouhei kissing together.
Oka is rather very short (only 143cm tall), and she has a body which resembles that of an innocent little girl, yet she has a quite large breasts and hourglass figure like that of a fashion model, giving healthy boys like Tsubaki, mixed feelings about her appearance.
Oka has remarkable self-worth and self-confidence. She can be bold and intimidating in both her attitude and appearance. She seems to 'call the shots' in her relationship with her boyfriend, Ueno, and at times will dominate over him. However, at other times, she is willing and able to become subservient to him, thus causing Ueno to always be uncertain as to her mood and behavior. Although Oka and Ueno seem to have a typical girlfriend and boyfriend romance, secretly, they enjoy a playful, fun S&M relationship, with the two changing the master and slave roles frequently. Oka is also portrayed as being slightly devious, this given by her positive reaction and joy in peeking down Urabe's blouse one day, and seeing her lacy bra.
Oka is also a bit of an exhibitionist, as she likes to wear sexy, provocative clothing in public, much to the chagrin of Ueno. Although Oka likes to 'show off' by wearing her peculiar fashion style in public, she is actually entirely loyal to Ueno. This is seen when she had considered a shipping with Tsubaki, but declined in her mind to do so, as it would be distressing and unfair to Ueno. Oka is also somewhat competitive, especially in social and romantic situations. She wishes to always stay ahead of what Urabe and Tsubaki are doing romantically, as if it were a competition of sorts. However, Oka also has a strong sense of friendship, especially with Urabe who she shares a drool bond with, and considers the bonds of friendship to be unbreakable, even to the point that Oka likes to, at times, tease and spoof Urabe and Ueno.
Despite Oka's somewhat rebellious nature, she applies herself to her academic pursuits, and gets good grades and praise from her teachers. She even consents to regularly tutor Ueno, who only looks upon her study sessions as time to attempt to make-out with her. Without Oka's concern and empathy for Ueno's downward academic direction, he would probably fail high school.
Oka loves sweets, especially ice cream.
Oka attends the same High School, and is in the same classes as Urabe and Tsubaki. After she sees the drool-tasting ritual between Tsubaki and Urabe, she befriends Urabe, and tricks Urabe into sharing a girl-with-girl drool bond as well. Later, Oka very casually and slyly tastes Tsubaki's drool infused ice cream, and also forms a drool bond with him, afterall. She views her relationship with Ueno almost as leading competitors with Urabe and Tsubaki for social and romantic progress. Although in episode 6 of the anime she does "flirt" with Tsubaki by calling him by his first name and touching his face, which could lead some people to believe she might like him. However, she later tells Urabe in confidence that even though she was romantically attracted to Tsubaki, she decided that a relationship with him would be 'problematic', especially since she already has a somewhat jealous boyfriend, Ueno. However, Oka eventually forms a casual drool bond with Tsubaki, when she tastes ice cream that has been infused with his drool.
Oka has a passion for cos-play and possibily cross-cosplay. This can be seen from when she is offered to dress as a sexy French maid at the Hoshinome Cultural Festival, she is eager to do so, even to the point of helping out at the Maid Cafe. She rejoiced when high school boys wanted to take pictures of her at the Maid Cafe, although this sparked rabid jealousy in Ueno. Later, Oka, as a guilt offering, offers to wear the French Maid outfit out in public, with him on a date, calling him 'Master' all evening long. Ueno objects, but secretly is pleased at her devotion.