Fuwa Mitsuharu served as a bushō and retainer of the Saitō and Oda clans during the Sengoku and Azuchi-Momoyama periods.
There are assorted theories concerning the family lineage. Under one, Mitsuharu was a descendant of Fuwa Hayato Fujiwara Naoie; and, under another, the lineage began with Fuwa Hayato-no-suke, a name adopted by Matsui Naoshige, the son of Matsui Kurōdo Naoie who descended from Minamoto no Tameyoshi – the leader of the Seiwa-Genji family; and, finally, there is a theory that Matsui Naoie, from a hereditary line of Shinto priests serving the Nangū Shrine in Yamashiro Province, moved to the village of Fuchū in the Fuwa District of Mino Province and adopted the Fuwa surname.
Mitsuharu served as the lord of Nishinoho Castle in Mino Province and, from early on as a retainer of the Saitō clan, the sengoku daimyō of Mino. Along with Inaba Yoshimichi, Andō Morinari, and Ujiie Naomoto, Mitsuharu was known as one of the Western Mino Group of Four. Unlike the other three, Mitsuharu was said to have remained loyal to the Saitō until the end, but after the Saitō were eliminated, he served Oda Nobunaga.
Service as a retainer of Oda Nobunaga
According to one secondary source from the Genroku era in the Edo period, Mitsuharu went to Odani Castle in Ōmi Province, and, following consultations with a retainer of the Azai clan named Anyōji Keisei, arranged for the engagement of Nobunaga’s younger sister, Oichi, to Azai Nagamasa. Mitsuharu, along with Naitō Shōsuke, attended her bridal procession.
In the seventh month of 1568, after Nobunaga responded to pleas from Ashikaga Yoshiaki (who was under the protection of Asakura Yoshikage of Echizen) to march upon Kyōto, Mitsuharu, together with Wada Koremasa, Matsui Sadakatsu, and Shimada Hidemitsu, headed toward Echizen to meet Yoshiaki. After capturing Kōhoku in the battle for the capital, Mitsuharu was sent to meet Yoshiaki who was waiting at the Ryūshō Temple. Thereafter, Mitsuharu participated in the Siege of Ōkawachi Castle in the eighth month of 1569, an attack on Odani Castle in the sixth month of 1570, the Shiga Campaign in the ninth month of 1570, an offensive in Ise-Nagashima in the ninth month of 1571, an encirclement of enemy forces at Katano Castle in the fourth month of 1572, the Siege of Makishima Castle in the seventh month of 1573, and the Siege of Ichijōdani Castle in the eighth month of 1573. In 1574, after the killing of Maeba Yoshitsugu of Echizen, Mitsuharu deployed with Hashiba Hideyoshi and Niwa Nagahide to Tsuruga and, in the sixth month of 1574, participated in a subsequent offensive in Ise-Nagashima.
Service as a member of the Fuchū Group of Three
In the eighth month of 1575, Mitsuharu participated in the Echizen Ikkō-ikki. After this campaign, Oda Nobunaga awarded Shibata Katsuie control of eight districts in Echizen. Together with Sassa Narimasa and Maeda Toshiie, Mitsuharu governed two districts in Fuchū in Echizen while also serving as metsuke, or overseers, for Katsuie. These three individuals were referred to as the Fuchū Group of Three. Mitsuharu resided in Ryūmonji Castle in Echizen. Owing to ongoing battles against the Kaga Ikkō-ikki and Uesugi Kenshin, their service as yoriki, or security forces, for Katsuie, became increasingly notable. In the eighth month of 1577, each one of the Fuchū Group of Three joined in a battle to pacify ikki forces in Kaga under Katsuie as their commander-in-chief. In the second month of 1581, Mitsuharu joined Toshiie and others in the Kyōto Mounted Horse Parade as one of the bushō in the Echizen group led by Katsuie, but reports arrived that Uesugi Kagekatsu had invaded Etchū Province and surrounded Koide Castle, so those from the Echizen group under the command of Katsuie were ordered to deploy.
Nevertheless, Mitsuharu was not entirely wed to the command of Shibata Katsuie, mobilizing for the Saika Offensive from the second month of 1577, the Siege of Arioka Castle from the eleventh month of 1578, a deployment to Etchū and Kaga on 3/15 of 1581, and the Iga Offensive in the ninth month.
Mitsuharu died in Echizen Province, but there are various theories concerning the date, including 12/14 of 1580, 11/8 of 1581, after 1581, or around 1583. Mitsuharu was succeeded by his son, Fuwa Naomitsu.