Seiwa

Seiwa is a term that appears in Japanese history in several related contexts. It is most commonly associated with Emperor Seiwa, who is traditionally counted as the 56th emperor of Japan and who reigned during the Heian period in the 9th century. Details of his personal life are limited in early sources, but his name became linked to the imperial line of that era.

The Seiwa era (858–875) is another use of the name. This was a nengō, or era name, used during the early Heian period. Era names were chosen for political or symbolic reasons and were used to mark certain reign events and calendar cycles.

Seiwa Genji refers to a major branch of the Minamoto clan that traces its lineage to Emperor Seiwa. The Seiwa Genji claim descent from the imperial line through the maleline and became one of the most influential branches of the Minamoto dynasty. Members of this lineage played pivotal roles in late Heian and Kamakura period politics and warfare; among them are notable figures who contributed to the rise of the Kamakura shogunate.

In summary, Seiwa can denote (1) Emperor Seiwa, a 9th‑century emperor of the Heian period; (2) the Seiwa era, a specific nengō from 858 to 875; and (3) the Seiwa Genji, the Minamoto lineage descended from Emperor Seiwa, which produced several prominent samurai leaders in later centuries. The common thread is the association of the name Seiwa with imperial ancestry and its enduring influence in both court rank and samurai history.