Nikki no Ie (Houses with Diaries) (日記の家)
Nikki no Ie (Houses with Diaries) is a nickname used to describe noble houses whose members kept diaries recording events relating to their families, and who passed these diaries down from generation to generation.
Representative examples of such 'houses with diaries' include the Onomiya line of the Northern House of the Fujiwara clan, which had the "Chuyuki" (especially noteworthy is its entry for Novenber 12, 1091), and the TAIRA no Takamune line of the Taira clan (particularly the entry "Suberagi no moto" [Under the Emperor] in their "Imakagami"). In addition to these examples, the Kajuji line of the Fujiwara clan is thought to have come from the same high pedigree as them, and the same feature of diary-writing appears in the Imperial House as well as in the Sekkanke (the house of regents and advisors). The apparatus to manage official documents under the Ritsuryo system, namely the Gekikyoku (Secretaries' Office) and the Benkankyoku (Controller's Office), was dismantled in the 10th century, which led people to begin seeking to modify the precedents for etiquette and legal judgments of public ceremonies and events according to what was found in the written record as recorded in diaries; this meant that for the noble families of aristocratic society, who tended to own many such diaries and could now use them to defend their own pedigree according to past precedent, great importance came to be attached to diaries. As a result, during the Insei period (during which retired Emperors ruled), such families came to be called 'Nikki no ie' (houses with diaries), a nomenclature that mimicked earlier terms like 'Raku no ie' (musical houses) for those families historically famous for their musical accomplishment, as well as 'Kyuba no ie' (houses of fine archery and horsemanship) for families considered famous for their skill in the martial arts. In such "houses with diaries," beyond simply having the family head of each successive generation record and then maintain ownership of a diary, family members would also make manuscript copies, abridged versions, and indices (by topic or category) of the house diary, and gain a thorough understanding and knowledge of court practices through research into what was recorded therein; moreover, such families also tried to guard against the possibility of losing their house diaries by setting up a governmental system in which they themselves could serve the Imperial Court as officials or the Sekkanke (the line of regents and advisors) as keishi (clerks and household superintendents) and karei (house retainers), thereby aiming to keep their family name stable and secure.
For that reason, not only "houses with diaries" but all of aristocratic society during the medieval period depended on these diaries which each successive generation inherited as the 'foundations of knowledge,' and took the diaries to be the principal source for determining house territory and property, which was each family's 'economic base'; eventually the importance of these diaries as well as instructions on how to handle diary-related matters came to be recorded in such documents as the letter of transfer and the last will and testament given to each successor (the eldest son and heir) of each such family.