There is a theory that the ninja costume was made based on the working clothe used in Koga gun (county) region (present-day southeastern Shiga Prefecture) and Iga Province region (present-day western Mie Prefecture).
この衣装は、元々は甲賀郡地方（現在の滋賀県南東部）や伊賀国地方（現在の三重県西部）で使われていた野良着が元とする説がある。