Etymology and distribution of 古曾.

Koso 【古曾】^{レベル1
Very rare}  The Japanese surnames etymology dictionary.

Okayama-ken , Hyougo-ken . 直原 variant of. Okayama-ken Akaiwa-shi In Nakayama tells that it changed from the Naohara family name in 1593 (Bunraku 2 years). 直原 Jikihara reference. Hyougo-ken Akou-shi Kamakuya was in the Edo period in the Ako samurai of the clan office.