Yayoi is taller than the other teachers and has long black hair with straight bangs and a loose strand hanging in front of her face. She also has dark colored eyes. She has a vacant expression and smiles in a friendly manner from time to time. She exudes an aura of a witch, often dressing in dark tones of clothing.
She is fairly quiet and soft-spoken, made especially obvious next to her more extroverted daughter and husband. Though she seems to be emotionless and cold, she actually cares for Kirin and her husband Satoru very much and feels bad for leaving Kirin in Ryuuichi's care for a week. She is gentle and very close to her daughter.
She is dedicated to the drama club, leading to multiple attempts of persuading Ryuuichi and the rest to join. On one occasion, she hands over Kirin to the club for a week (with Ryuuichi responsible for her overnight care as well) because she needed to help her drama students practice for the Morinomiya Drama Festival.
Yayoi first met her husband Satoru when she was playing the lead role in a play while attending Morinomiya University. It is said by her classmates during this time that Yayoi was being scouted by movie directors to become an actress in films, though Yayoi wanted to pursue a career in education. Backstage, an acquaintance of Satoru took him to find a subject for his photography entry, in which Satoru began to berate Yayoi saying that her acting wasn't good at all that that other than the fact that she was " a little pretty" there was nothing special about her at all and began to flirt with other female members of the cast. Though troubled by his words, Yayoi performed for the three last days of the play and noticed that Satoru, on every one of those days, was in attendance in the back, watching. When he finally clapped for her at the end of her performance, Yayoi was so overcome with happiness that she began to smile, shocking Satoru and making him bashful in her presence. Sometime after, she ended up marrying Satoru and had their daughter Kirin.