The sister or the child of Soukoku?

Kouyou had always been a guiding light for Chuuya's younger sister, Kyomi, taking care of her like a mother. But when their lives takes a cruel turn and Kouyou suffers an injury, everything changes in an instant. Suddenly, the one person Kyomi relied on the most is unable to care for her any longer.
With no one else available to step in, Chuuya and his husband, Dazai take care of her.
They act like true siblings.
No - like a true family...