Although relics of swords from the early Heian period are scarce, and the transition of styles or how and when Japanese original curved swords were formed are not fully figured out academically, after the mid Heian period (around the 10th century), when the turmoil of Johei and Tengyo occurred, Warabiteno Katana (curved sword) which was easy to use when riding with its warped body of blade was used instead of conventional straight swords.
平安時代初期の刀剣の遺品は乏しく、作風の変遷や、いつごろどのようにして日本独自の湾刀が形成されたかについては、学問的に十分解明されていないが、承平天慶の乱などが発生した平安時代中期以降（10世紀ころ）従来の直刀に代わって騎乗時に扱い易い刀身に反りのある蕨手刀（彎曲刀）が使用されるようになった。