" 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 friend. She was first introduced when Tsubaki walked into an empty classroom to see her and Kouhei kissing together. She is rather short (143cm tall), and she has a body which resembles that of an innocent little girl, yet with a big bust like that of a fashion model. She seems to enjoy, on occasion, showing off her body, when she dresses in her favorite clothes, many times of a somewhat provocative style, much to the chagrin of her boyfriend.
After she sees the drool-tasting ritual between Tsubaki and Urabe, she befriends Urabe, and it's revealed that they share a girl-with-girl drool bond as well. Oka is portrayed as slightly devious, given by her positive reaction to peeking down Urabe's blouse. 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.