Kōzai

The Kōzai of Sanuki claimed descent from the Northern House of the Fujiwara through the Sanuki Fujiwara. After the Jōkyū War of 1221, Nii Sukemura, a kinsman of their forebear Fujiwara no Sukemitsu, received lands in Kagawa and Aya, built Shōga Castle and took the surname Kōzai.

The house became the greatest kokujin power of eastern Sanuki and served the Hosokawa. In the Ōnin War its head Motosuke fought for Hosokawa Katsumoto and was counted among the Four Heavenly Kings of the Hosokawa. The family split into an upper line in Kyoto and Yamashiro and a lower line in Sanuki.

Under Motosada the lower line commanded the Shiwaku fleet and traded with Korea in 1531. The last head Yoshikiyo surrendered to the Chōsokabe in 1582 and fought against Hideyoshi's Shikoku invasion in 1585, after which he lost his fief.