Mansai's father was Juichii (Junior First Rank) Dainagon (grand councilor) Morofuyu IMAKOJI, and Mansai's mother was Shirakawadono who was a daughter of Geni, Bokan (a priest who served for the families of Monzeki (temple formerly led by founder of sect, temple in which resided a member of nobility or imperial family)) Hoin (the highest rank among Buddhist priests) of the Seigoin Temple, and served Nariko HINO, the legal wife of Yoshimitsu ASHIKAGA, the third Shogun of the Muromachi bakufu (Japanese feudal government headed by a shogun).
父は従一位大納言今小路師冬、母は聖護院房官法印源意の娘で室町幕府3代将軍足利義満の室日野業子に仕えた白川殿。