Shimazu Nariakira
Nagahiro was the ninth son of Shimazu Shigehide, lord of Satsuma Domain; Kuroda Narikiyo, lord of Fukuoka, adopted Nagahiro in 1822 later Nagahiro married Narikiyo's daughter, Sumihime. Nagahiro's mother was a woman of humble origins named Chisa; she had attracted Shigehide's attention with her "sturdy build and great love of sake." Much like his mother, Nagahiro was also well-built. He was close in age to Shimazu Nariakira, and the two had a brotherly relationship. His childhood name was Momojiro (桃次郎).