She is a student of Kunugigaoka Junior High School. She is assigned to Class 3-E, where she trains to become a professional assassin, with her teacher as the target.

Yukiko is diligent, ladylike, and cordial; although she does not particularly stand out, she is popular with her classmates. A very considerate individual, she had, on one occasion, volunteered to buy drinks for everyone in her class. Yukiko is deliberative and an excellent organizer. She was responsible for structuring the schedule for Class 3-E's trip to Kyoto, and her work had impressed Korosensei. Furthermore, she is adept in considering all factors before making a decision, which is why she had chosen the virtually unoccupied Gion District as the ideal setting for the assassination to take place.