Asauchi

Bearing a name that translates as Shallow Hit, an Asauchi is a Zanpakutō without a name, handed to Shinigami who have yet to prove themselves. That title speaks to the sharply diminished strength of a sword whose bearer has not properly bonded with it. Ōetsu Nimaiya forges every last one, and across the entire history of Soul Society not a single Shinigami has ever awakened a real Zanpakutō without first wielding one of his Asauchi. Because he made them all, Nimaiya can pinpoint where any blade in existence lies, and Ichibe'e Hyōsube possesses an innate knack for knowing the genuine name of anything, so he recognizes every sword's name the very moment it passes to a Shinigami.

Plain as they look, Asauchi count as the supreme Zanpakutō, since any of them can potentially become absolutely anything. The Gotei 13 numbers more than six thousand, and each recruit is lent one of these nameless swords on arriving at the Shin'ō Academy, then formally granted the same weapon upon assignment to a division. A Shinigami must never let the blade leave their side, and as training advances they steadily transfer the character of their spirit into it, shaping a Zanpakutō all their own. Made to appear, an Asauchi looks like a featureless humanoid marked only by two little mouths standing in for eyes, gaining traits and a personality solely as its owner leaves an impression on it. Where a Shinigami already holds a fully awakened spirit, the Asauchi instead serves as a catalyst, coaxing that spirit out and being absorbed in the process.

Not everyone receives their blade the usual way. Kenpachi Zaraki, who never enrolled at the academy at all, simply claimed the Asauchi of a slain Shinigami and forged his own path with it. Kaname Tōsen likewise inherited the Asauchi of a fallen comrade and reshaped it into his Zanpakutō, Suzumushi. Since Nimaiya is the maker of them all, he can find any Zanpakutō anywhere, while Ichibe'e Hyōsube knows each one's name the moment it is issued. The Ise Clan forms an exception: bound to their inherited sword Shinken Hakkyōken, its members can never impress themselves upon an Asauchi.