Tosa, Historic region of the Japanese island of Shikoku. It dates at least to the Heian period, when Ki no Tsurayuki (868?–945?), editor of Japan’s first imperially commissioned poetry anthology, wrote a fictional diary drawing on his experiences as governor of Tosa. In 1571 it became a unified domain (han) whose daimyo opposed Tokugawa Ieyasu when he consolidated his control of Japan in the early 17th century; this historical enmity became important at the time of the Meiji Restoration (1868), when samurai from Tosa, like those from Satsuma and Chōshū, helped overthrow the Tokugawa shogunate. See also Itagaki Taisuke; Tokugawa period.