Genya was born into the Shinazugawa family, one of the honorable families in the Demon Slayer Corps. However, his childhood was not happy. His father was a cruel person and often beat his mother. He and his older brother, Sanemi, had to work hard to protect their younger siblings. One day, the devil attacked his house. The devil killed his mother and younger siblings. He and Sanemi managed to survive, but Sanemi lost his left eye. This incident made him very angry and sad.