Kabashira is sealed as a very large katana, possibly even an Odachi. This is a sharp contrast to the set of daggers is becomes in its Shikai.
The Shikai takes the form of five daggers with blades that are slightly rippled. When the Release Command "Annoy" is said, the sword glows and shrinks into a dagger, splitting into five in the user's hands.
The daggers can be used for cutting and stabbing. But their main purpose is to be thrown. When thrown at the enemy, they do little more than a normal thrown dagger. But when the dagger stabs into the opponent's shadow when thrown at the ground, the opponent's movements are slowed to a crawl until either the knife is removed from their shadow or their slowed movement eventually moves the shadow away from where the knife stabbed. Not only is the user's body slowed down, but their mind is slowed down as well. When the knife is removed or the user's slowed movements escape the knife, it will seem as if everything has jumped forward.
The downside, however, is that the knives can be used against the user. If the user misses when a dagger is thrown, the enemy can pick up one of the daggers and use it to stab the user's own shadow, making them the victim of their own Zanpakutou's effect.
The Zanpakutou's spirit takes the form of a giant mosquito with a swarm of regular-sized mosquitoes surrounding it.