Kōsaburō Shirakawa, originally named Masakazu Shimizu, is married to Atarashi Shiori, the eldest daughter of Suou Shirakawa. This marriage integrated him into the esteemed Shirakawa acting dynasty as son-in-law to Shirakawa Kaou XV, a legendary kabuki actor and Living National Treasure. His position within this family brings him into proximity with Sarasa Watanabe, Shirakawa Kaou XV's secret illegitimate daughter. Their connection initially fueled rumors that Sarasa was Kōsaburō's illegitimate child, though she is actually his wife's illegitimate sister, making her his sister-in-law. As a kabuki actor, he operates within the Misatoya Acting House, a prominent institution headed by Shirakawa Kaou XV. His role in this artistic environment intersects with the sphere of the Kouka Revue Company, particularly through Sarasa Watanabe's ambitions and familial ties.