Because his father Nobunori ITAGAKI was punished by being deprived of his fief and later executed, Masanobu moved to Inui village, Shuchi County, Totomi Province to stay inside his home, and changed his family name to Inui.
父板垣信憲が改易ののち誅されたため、遠江国周智郡乾村に籠居して乾氏に改めた。