Lifespan: Tenshō 12 (1584) to 1;30 of Keian 3 (1651)
Title: Governor of Oki
Clan: Ninomiya (an illegitimate branch of the Hemi clan from the line of Minamoto no Yorinobu of the Seiwa-Genji) → Kadota
Lord: Mōri Terumoto → Mōri Hidenari
Father: Ninomiya Naritoki
Mother: Daughter of Kadota Mototada
Siblings: Mototsune, Yada Tsuneyuki, sister (wife of Zaima Motohisa), sister (wife of Nakamura Mototoshi), sister (wife of Hirasa Motosada), sister (wife of Satake Motoyoshi)
Wife: Daughter of Kodama Motokane
Children: Motohisa, daughter (wife of Amano 元処), Motoyasu, daughter (wife of Kaneshige Kagetsune), daughter (wife of Mōri Narisada), daughter (wife of Sugi Nariyuki)
Adopted Children: Daughter (natural daughter of Kawamoto Shinbei, wife of Zaima Motonao)
Kadota Mototsune served as a bushō during the Azuchi-Momoyama and early Edo periods. He was a retainer of the Mōri clan and, in the Edo period, the Chōshū domain. His family was a member of the ōgumi, or group of families of higher pedigree serving as direct retainers of the Mōri.
In 1584, Mototsune was born as the eldest son of Ninomiya Naritoki, a retainer of the Mōri clan serving as a close associate of Mōri Terumoto. He had the common name of Kodenji.
On 6/15 of Bunroku 4 (1595), Mototsune received a written declaration of his crowning from Terumoto and attended his coming-of-age ceremony. At this time, he received one of the characters from the name of Terumoto, adopting the name of Mototsune. The name on the declaration was Kadota Kodenji, indicating that as of the time of his coming-of-age ceremony, Mototsune was already using the surname of his mother. On 12/26 of Keichō 8 (1603), Mototsune, along with his father, Naritoki was conferred the name of Tarōemon-no-jō, or Lieutenant of the Outer Palace Guards of the Right Division, from Terumoto.
Upon Naritoki’s death on 5/3 of Keichō 12 (1607), Mototsune succeeded him. Mototsune served as the head of the ōgumi, a band of direct retainers of the Mōri in the Chōshū domain. On 10/16 of Genna 6 (1620), Mōri Hidenari gave Mototsune a list of seventeen prohibitions on the lives of persons serving under the command of members of the ōgumi.
Beginning in 1624, Mototsune led members of the ōgumi band of retainers to perform the second phase of construction for Ōsaka Castle. In preparation for this role, on 3/28 and 12/16 of Genna 9 (1623), he received instructions from Hidenari with respect to the stipends and loans of those serving under the command of the members of the ōgumi.
According to a document dated 8/13 of Kanei 2 (1625) jointly signed by Masuda Motonaga, Shimizu Kageharu, and Shinji Motokane, Mototsune had landholdings of 1,500 koku comprised of 1,000 koku in the village of Kama in the Mine District of Nagato and 500 koku in the Shiromatsu manor in the Yoshiki District of Suō Province. On 12/13 of Kanei 3 (1626), Mōri Hidenari conferred upon him the honorary title of Governor of Oki.
On 12/30 of Keian 3 (1650), Mototsune died at the age of sixty-seven. He was succeeded by his eldest son, Motohisa.
The traditional elongated gate to the remains of the residence of his descendants continues to exist in the urban area below Hagi Castle.