蕨手刀 - Wikiwand

The direct predecessor of the tachi (太刀) has been called Warabitetō (ja:蕨手刀) by the Emishi (Not to be confused with Ainu) of Tohoku. The Nihonto Meikan

Chokutō

Kenukigata-tachi (ja:毛抜形太刀), which was made by improving Warabitetō (ja:蕨手刀) used by Emishi in Tohoku region. And Kenukigata-tachi evolved into tachi

Japanese swordsmithing

swords. The predecessor of the Japanese sword has been called Warabitetō (ja:蕨手刀). In the middle of the Heian period (794–1185), samurai improved on the Warabitetō