Yamabiko (tool)

Yamabiko (山彦, Literally meaning: Mountain Echo) is the special blade weilded by expert — Seigetsu Uchiha. The blade is hidden underneath Seigetsu's kimono and haori. This allows Seigetsu to pull the blade out at any point of a battle completely catching an opponent off guard.

The blades power is simple, but unexpected to anyone who has never crossed paths with it. As he swings his blade, those that are able to evade the slashes, are still hit. This is because of the special ability of the blade, which allows it to cut the opponent with the left behind forces. Daiki Mazuka has explained the mechanics of this technique exactly like this: Yamabiko is swung, an opponent evades the attack. Though, because of the left behind force of the swing, the wave of air is still launched at the target, cutting them just as if they were cut by the blade itself. It is made of some unknown material, but after trying to alter it with his control over metals, Seigetsu found that it isn't made of metal.

It was initially found in the mountains of Yamagakure when Seigetsu was just a young boy. His many journeys with K'un led him to the location of this blade. Though, because he wasn't mutually strong enough to wield it just yet, it was placed into a scroll. K'un has stated that the blade feeds off of Seigetsu chakra, the only one worthy of weilding the blade.

Influences
The blade's "wind cutting ability" and name are both greatly influenced by the Japanese mountain god  (山彦). This wind that is explained, is actually the echo of the blade being swung giving the wielder a second chance at scathing their opponent.

Trivia

 * The Yamabiko is stated to have various different forms. Though, the one shown in the image of the tool is the only form shown by Seigetsu, other than it's basic katana look.