Motohiro participated in the Genpuku (Coming of Age) ceremony in January 1655 (December 1654, in old lunar calendar) at which time he was granted the rank of Shogoinoge (Senior Fifth Rank, Lower Grade Rank), and became Sakone gon no shosho (Provisional Minor Captain of the Left Division of Inner Palace Guards).
承応3年（1654年）12月に元服して正五位下に叙せられ、左近衛権少将となる。