Kotoko Yotsuya appears in the OVA "15 Bishōjo Hyōryūki" as one of fifteen girls stranded on a deserted Pacific island with the male protagonist, Kazuma Shiraishi. She is Kazuma's reliable and caring childhood friend, known to him as "Kazu." Living next door and attending the same school, their friendship traces back to early childhood. Kotoko possesses violet hair, lilac eyes, stands 158 cm tall, and has measurements of 82-55-81. Her birthday falls on December 28, and she has blood type A.

Cheerful and kind, Kotoko openly expresses deep affection for Kazu. She eagerly poses for his camera during their frequent photography sessions and maintains a diary documenting their relationship. Her signature phrase, "Only if it's Kazu-chan... Okay," reflects her consistent willingness to accommodate his requests.