These Zanpakutō Spirits emerged from the Zanpakutō of rank-and-file Shinigami, and went rampant once their masters were killed, after failing to force them into submission. Normally, a Zanpakutō dies when its master dies, but these rampant Zanpakutō Spirits suffer an emptiness at the realization that they no longer have a master, and thus no true identity, which results in an abnormality that has them exhibiting berserker rage-type behaviour.