Giyu is a young 4 year old and his sister is killed by a demon while she was protecting her little brother, Giyu, he was traumatized and he was in his house and his sister's dead body. Giyu and Tsutako's parents died from illness and Giyu was alone in his house until your parents helped him and buried his sister near Giyu's house, Giyu was brought into your estate and he can live there as long as he want