Oshika Norimitsu served as a bushō during the late-Muromachi period.

Norimitsu was born as the son of Oshika Noriyori.  Noriyori was the son of Imagawa Norimasa, the fourth head of the Imagawa family.  Norimasa desired Noriyori to succeed him as the head of the clan, but after a succession struggle between Noriyori and his older brother, Imagawa Noritada, the Muromachi bakufu issued a verdict for Noritada to inherit the headship of the clan.  As a result, Noriyori resided in the environs of Sunpu in Oshika.  He then adopted the surname of Oshika.

There is a theory that Norimitsu’s mother was the daughter of Uesugi Masanori, the deputy of Ashikaga Masatomo, the Horigoe kubō.  The traditional view that Noriyori’s mother (i.e., Norimitsu’s grandmother) was a sister of Uesugi Mochisada of the Ōgigayatsu-Uesugi family is inaccurate and there are in fact no historical records in regard to Norimitsu’s mother.  Meanwhile, Mochisada and Masanori both used the same name of Jibu-Shōyū.

In the fourth month of 1476, Norimitsu’s older cousin, Imagawa Yoshitada (the sixth head of the Imagawa family), attacked kunishū, or provincial landowners, in Tōtōmi Province including Yokochi Shirōbei at Yokochi Castle and Katsumata Suri-no-suke at Katsumata Castle.  While returning to Suruga, at the Battle of Shiokaizaka, Yoshitada was attacked and killed by remnants of these clans.  At this time, Tatsuōmaru (later known as Imagawa Ujichika) was still only six years old so retainers including the Miura and Asahina clans backed Norimitsu, triggering a succession struggle.  The faction supporting Tatsuōmaru engaged in a flurry of battles against the faction backing Norimitsu.  Meanwhile, the Yokochi and Katsumata clans who were responsible for the death in battle of Yoshitada colluded with the Shiba clan and served Shiba Yoshisuke (later known as Shiba Yoshihiro) the military governor of Tōtōmi formally appointed by the bakufu.  By obstructing them, Yoshitada was viewed as a rebel toward the bakufu so rather than have his orphan, Tatsuōmaru, succeed to the headship of the clan, there was a possibility that he would be eliminated as a family member of a rebel.  Consequently, Tatsuōmaru’s mother, Kitagawa-dono, took him and fled for the protection of Hasegawa Masanobu, a wealthy landowner serving as the lord of Kogawa Castle.

Uesugi Masanori and Ōta Dōkan, the head of house affairs of the Ōgigayatsu-Uesugi family, led forces to occupy Suruga and then intervened in the succession struggle in the Imagawa clan.  Fearing that the authority of the deputy shōgun of the Kantō would extend to Suruga, the bakufu dispatched Tatsuōmaru’s uncle, Ise Shinkurō (Moritoki), to mediate between the factions.  These efforts yielded an agreement whereby Norimitsu would serve as the guardian of Tatsuōmaru to represent the clan.  Masanori and Dōkan withdrew their forces.  Around the time that Shinkurō is surmised to have been a lowly rōnin, or wandering samurai, this was regarded as the first step in the rise of the brilliant strategist later known as Hōjō Sōun.  Based on recent research, this is determined to have been Ise Moritoki, a member of the Ise clan and direct retainer of the bakufu who, upon the wishes of the bakufu, traveled from the capital to Suruga to mediate an internal dispute of the Imagawa family.  As a proxy for the head of the clan, Norimitsu entered the Imagawa (Sunpu) mansion although details of his service as the proxy for the head of the clan are sparse.  Meanwhile, Tatsuōmaru and his mother, Kitagawa-dono, moved to the residence of the Saitō clan at Mariko Castle in Suruga.  In 1479, Moritoki petitioned the bakufu and obtained an official letter in the name of the prior shōgun, Ashikaga Yoshimasa, authorizing Tatsuōmaru as the successor to the Imagawa clan.  

Years later, although Tatsuōmaru reached the age of fifteen and became an adult, Norimitsu did not attempt to transfer the headship of the clan to him.  Instead, he took steps to suppress Tatsuōmaru and forcibly claim the role for himself.  In 1487, Kitagawa-dono and Tatsuōmaru requested help from Moritoki who was serving Ashikaga Yoshihisa, the ninth shōgun of the Muromachi bakufu in Kyōto.  Moritoki then went to Suruga again.  In the eleventh month, Moritoki gathered soldiers at Ishiwaki Castle to storm the Imagawa mansion.  Norimitsu then took his own life without a fight.  Norimitsu had depended upon Ōta Dōkan for defense, but Dōkan was earlier killed by Uesugi Sadamasa.  Ashikaga Masatomo, the Horigoe kubō, appears to have switched his position to support Tatsuōmaru in view of his relationship with the bakufu.  Norimitsu’s nephew, Oshika Magogorō, also took his own life so the Oshika clan confronted the prospect of being extinguished.  After attending his coming-of-age ceremony and changing his name to Ujichika, he promoted Minbu-no-shō, the illegitimate younger brother of Magogorō, to serve as the head of the Imagawa goikka, aiming to draw support from the former members of Norimitsu’s faction.  Minbu-no-shō was permitted to use the Imagawa surname on an exceptional basis.  In the era of Imagawa Noritada, persons outside of the main branch of the Imagawa were prohibited by the bakufu from using the Imagawa surname, thereby treating the surname as exclusive.  The main branch of the Imagawa recognized their special status based on the limited possibility that Norimitsu and his family could succeed to the headship of the Imagawa clan.  Alternatively, it is questioned whether such a prohibition originally existed.

According to one scholar, the decision by the Muromachi bakufu to have Norimitsu serve as the proxy for the head of the Imagawa clan was an outcome of the death of the prior head of the clan, Imagawa Yoshitada, which circumstances the bakufu regarded as traitorous.  Moreover, there was a possibility that Tatsuōmaru would also be tracked down and killed (on the premise that Moritoki traveled from the capital to Sunpu with the aim to protect Tatsuōmaru as a member of the family of a traitor) and, further, that the decision was supported by Ōta Dōkan.  Nevertheless, in 1486, Dōkan was assassinated so, having lost his patron, Norimitsu witnessed a weakening of his authority.  In view of the situation, Moritoki garnered the support of kokujin in Suruga and succeeded in having Tatsuōmaru become the next head of the clan.

Character

In historical accounts of the Imagawa family, Norimitsu is praised as an individual who demonstrated exceptional military prowess.