Kousaburou Shirakawa, born Masakazu Shimizu, is a kabuki actor married to Shiori Atarashi, the eldest daughter of the legendary kabuki actor Shirakawa Kaou XV. He performs within the prestigious Misatoya Acting House alongside his father-in-law. His marriage to Shiori makes him the brother-in-law of Sarasa Watanabe, the series' main protagonist, as Shirakawa Kaou XV is Sarasa's biological father, correcting an earlier misconception that portrayed Kousaburou as her father.

Professionally dedicated to kabuki theater, Kousaburou holds a significant position connected to the succession plans for the Shirakawa name. Shirakawa Kaou XV's grandson, Akiya Shirakawa (born Hiroshi Atarashi), is the heir-apparent destined to become the sixteenth Shirakawa Kaou. Kousaburou extends his influence into personal matters, advising Akiya on his relationship with Sarasa; he pragmatically suggests that transitioning from childhood friends to dating could preserve their bond despite distance. He implies that Akiya's romantic choices could affect Shirakawa Kaou XV's decisions regarding the succession, reflecting his awareness of the interplay between personal relationships and professional standing in the kabuki world. His presence contextualizes Sarasa's familial connections and the kabuki influences shaping her journey at the Kouka School.