Japanese emperor oak Japanese emperor oak acorn Japanese emperor oak leaf The Japanese emperor oak is a common tree in Tokachi. It was used by the Ainu to make the pillars of houses, and various other uses. The nisew (acorns) were peeled after their astringent taste was removed. They were then steamed, dried, and stored. When they were eaten, they were soaked in water, mashed together with oil, salt, or beans, boiled with fish, and eaten. In addition, in Obihiro, this species was called komnisirkorkamuy (“the god of the Japanese emperor oak which protects the land”), and this god was enshrined at the nusa (altar).