Utsuro (samurai family) (洞 (武家))
Utsuro was a quasi family-related community from the late Muromachi period to the Azuchi-Momoyama period that organized family members and vassals around the head of the family, called soryo (heir); organizations such as these were seen among Sengoku daimyo (Japanese territorial lord in the Sengoku period) in the Tohoku and Kanto regions. Utsuro, also called 'Kachu,' was the equivalent of a Bunkoku (a province that was governed by a Shugo daimyo (Japanese territorial lord as provincial constable) or Sengoku daimyo in an integrated fashion) that was seen in other regions. It is believed that Utsuro disappeared during the process of a reorganization in Bakuhan taisei (the feudal system characteristic of the shogunate) with the appearance of Kinsei daimyo (daimyo of the early modern era).
Summary
Within these regions, more than one daimyo family developed from traditional samurai groups existed in a ryoseikoku (province) with complicated territorial relations. Under such circumstances, a daimyo subjected their families, vassals, Kokujin ryoshu (local samurai lords) and jizamurai (local samurai) of neighboring provinces to their rule and asserted their superiority as a soryo (heir). They treated the vassals and Kokujin ryoshu, who had no blood relations, as equals to family members by conferring them the title of 'ikka' or 'ichimon' in an attempt to maintain their leading position in the organization.
This sort of organization was established by such clans as the Satake clan, Utsunomiya clan and Oda clan, and the words '当洞' (todo) or 'OO 洞中' (OO dochu) were used in the documents and letters of diplomatic negotiations exchanged between daimyo (Although the daimyo of the Mori clan, who was the daimyo of the western region of Japan, had a similar organization and also used the character '洞' in their documents, it is considered to be an exceptional case). By contrast, this phenomenon was not seen in the Takeda and Imagawa clans, which had achieved ichien shihai (integrated rule over whole territory) when they were still in the stage of Shugo daimyo; nor was it seen in the Gohojo and Satomi clans which were a newly emerged foreign power.
Utsuro' of the Date clan
The form of Utsuro is observed most characteristically in the Date clan. Tanemune DATE sought to organize an even larger Utsuro by integrating the Ashina clan, the Mogami clan, the Tamura clan, the Shirakawa Yuki clan, the Iwaki clan and the Soma clan through marriage and/or adoption. This was not particular to the Date clan, since Utsuro of the Sengoku daimyo families in this region are considered to have developed into daimyo ryokoku (territories ruled by daimyo) by integrating many small-sized Utsuro of Kokujin ryoshu in neighboring regions. "Jinkaishu," a bunkokuho (a law individual Sengoku daimyo enforced in their own domains) established by Tanemune, stressed the notion of Utsuro. Ironically, however, the extensive Utsuro built by Tanemune was dissolved due to the Tenbun War which had been caused by Tanemune himself, and many Utsuro that Tanemune had subjected to his rule followed the path to become independent Sengoku daimyo. The reason why this internal war was also called 'The Utsuro War,' was because those who participated, the vassals of the Date clan as well as the Ashina, Mogami and Soma clans, who were generally regarded as independent Sengoku daimyo, were members of Date's Utsuro at the time of the war.
Families and vassals of the Date clan who remained in the Utsuro even after the war were reorganized by Tanemune's great-grandson Masamune DATE into a group of vassals in the Sendai Domain, supported by the strict relationship between lord and vassal. Nevertheless, however, titles representing family status in the Sendai Domain that had been derived from the relationship of lord and vassal in the era of Utsuro, such as 'ikka' and 'ichimon,' were continuously used and became the basis of the hierarchical relationship in the domain (Allegedly, only the Katakura family, which became famous due to Kojuro KATAKURA, and one other family were conferred the title of 'ikka' and 'ichimon' or higher during the period between the end of the Tenbun War and the establishment of the Sendai Domain). Later on, these circumstances became a source of trouble for the Kinsei daimyo of the Date clan and the Sendai Domain, and caused various problems including the Date riot and the Boshin War.