Lifespan: Daiei 1 (1521) to 5/18 of Tenshō (1590)
Other Names: Chōmatsumaru (childhood), Eirin (monk’s name), Nakano-dono, Dewa-dono
Rank: sengoku daimyō
Title: Junior Fourth Rank (Upper), Master of the Office of Palace Repairs, Governor of Dewa
Clan: Nakano → Mogami
Bakufu: Muromachi – Commissioner of Dewa
Father: Nakano Yoshikiyo
Adoptive Father: Mogami Yoshisada
Siblings: Nakano Yoshimasa, Yoshimori
Wife: [Formal] Renshinin
Children: Yoshiaki, Nakano Yoshitoki (?), Nagatoro Yoshiyasu, Tateoka Akinao, Yoshihime, daughter (wife of Ayukai Tadamune (Munenobu)), Ganshōin
Mogami Yoshimori served as a sengoku daimyō during the Sengoku period. He was the tenth head of the Mogami clan of Dewa Province.
In 1521, Yoshimori was born as the second on of Nakano Yoshikiyo, the lord of Nakano Castle. Although an illegitimate branch of the Mogami, the Nakano clan produced heads of the Mogami clan on several occasions.
Yoshimori was the father of Mogami Yoshiaki, a daimyō and the eleventh head of the Mogami, and the maternal grandfather of Date Masamune, a sengoku daimyō of Dewa and Mutsu provinces and the seventeenth head of the Date clan.
In 1520, the year before the birth of Yoshimori, Mogami Yoshisada, Yoshimori’s great-grandfather and the ninth head of the Mogami clan, died without an heir. Yoshisada’s brother-in-law, Date Tanemune, then plotted to make the Mogami a puppet regime under the control of the Date. That same year, after Kaminoyama Yoshifusa, the lord of Kaminoyama Castle, rebelled against the Date family, Tanemune used this event as a pretext to take control of multiple locations in Dewa including Kaminoyama, Yamagata, Tendō, and Takadama. In 1521, owing to their refusal to pledge fealty, he attacked the Sagae clan on the western shore of the Mogami River.
At this time, the Date army brought together forces from Kasai, Sōma, Iwaki, Aizu, Miyagi, Kokubun, and Mogami. Although Tanemune settled with kokujin, or provincial landowners, from the surrounding area and brought them under his command, he encountered resistance from these kokujin with respect to naming the successor to the Mogami clan. In an effort to pacify the kokujin, he compromised and, in 1522, received Yoshimori from the Nakano clan as the next head of the Mogami. Yoshimori inherited the headship of the clan at the age of two. This year, during an invasion by Tanemune, Tendō Yorinaga, acting as his ally, burned down the Risshaku Temple.
In 1535, Yoshimori endeavored to revitalize the Mogami territory including the reconstruction of the Risshaku Temple after its destruction by Yorinaga. Around this time, the Mogami clan had in fact yielded their allegiance to the Date. In 1542, after the outbreak of a succession struggle between Tanemune and his eldest son, Date Harumune, known as the Tenbun Conflict, Yoshimori, with the support of senior retainers including Ujiie Sadanao and Yagashiwa Naoie (Sagami-no-kami), participated on the side of Tanemune. After recapturing Hasedō Castle, Yoshimori aimed to expand his powers and achieve independence from the Date. He then advanced into the Nagai District but, after the Ashina clan switched sides to Harumune, the situation reversed and Yoshimori also sided with Harumune. In 1548, Harumune finally emerged as the victor in his prolonged conflict with Tanemune.
In 1543, the Risshaku Temple received an eternal flame from the Enryaku Temple on Mount Hiei. In 1546, Yoshimori’s eldest son and designated heir, Yoshiaki, was born. Around this time, Sagae Kanehiro based on the western shore of the Mogami River and the Daihōji clan based in the Shōnai region, along with an influential figure named Tosabayashi Zentō operating under their command, took steps toward forming an alliance. However, based on a letter from Zentō to the Sagae, in the end, this failed to materialize. In 1560, seeking to expand his power, Yoshimori attacked Sagae Kanehiro, the lord of Sagae Castle, but this did not yield results. This year, Yoshimori dispatched a messenger to Ashikaga Yoshiteru, the fourteenth shōgun of the Muromachi bakufu, and received permission to give Yoshiaki one of the characters from the name of Yoshiteru. In 1561, as an expression of thanks, Yoshimori presented Yoshiteru with a falcon. In 1563, Yoshimori and Yoshiaki traveled to Kyōto and met with Yoshiteru. On this occasion, they were met at the palace of the shōgun. Yoshimori had Yoshiaki receive, as his formal wife, the daughter of a family member named Ōsaki Yoshinao and, around 1564, wed his daughter, Yoshihime, to Date Terumune. In 1567, Date Masamune was born.
Around 1570, a dispute arose between Yoshimori and his eldest son and designated heir, Yoshiaki. In the fifth month, Yoshiaki prayed at the Risshaku Temple for his succession to the headship of the clan, and, through the mediation of a senior retainer named Ujiie Sadanao, the father and son reconciled. In the eighth month, Yoshiaki inherited the headship. (Under an alternate theory, Yoshimori had already retired and entered the priesthood during the Eiroku era (1558 to 1570)). In 1571, Yoshimori entered the priesthood and adopted the name of Eirin.
In the first month of 1574, after conflict between the two reignited, the Date sought to suppress Yoshiaki for exhibiting a tendency toward independence. On the pretext of supporting Yoshimori (his father-in-law), Date Terumune deployed forces to the Mogami territory, giving rise to the Tenshō Mogami Conflict. Provincial landowners including Tendō Yorisada, Shiratori Nagahisa, and Nobesawa Mitsunobu sided with Yoshimori and Terumune, assaulting the Sagae clan aligned with Yoshiaki. Thereafter, the Sagae supported Yoshimori and a settlement was reached to the advantage of Yoshimori. Nevertheless, Yoshiaki launched separate attacks against those supporting Yoshimori, after which the Sagae clan switched sides back to Yoshiaki. On 9/10 of Tenshō 2 (1574), a settlement was reached with the Date on terms favorable to Yoshiaki, whereupon the Date forces withdrew from Dewa.
The conflict between Yoshimori and Yoshiaki persisted, but, in the eleventh month, through the intervention of Shiratori Nagahisa, the two sides settled and Yoshimori retired to the family temple known as the Ryūmon Temple.
On 5/18 of Tenshō 18 (1590), Yoshimori died at the age of seventy. Owing to the memorial service for his father, Yoshiaki was significantly delayed in deploying for the Conquest of Odawara, but, through the offices of Tokugawa Ieyasu, his rights to his landholdings were recognized.