Himura's Zanpakuto

Himura Morimiya's Zanpakuto is a very rare spirit weapon formed of two swords - even more special as it is two separate blades even when sealed. Their name is Kotori Asobi (Lit. "Little Birds Play")

Zanpakuto Basics
Himura's zanpakuto is sealed as a katana and wakizashi daisho pair. Originally they were sealed as a wakizashi and a tanto-sized blade, but as Himura's spirit power grew so did the swords. He is adept at wielding one or both of the blades at any given time.

When released they take the form of a pair of khopesh-like swords, though they retain their katana-style hilts. They are primarily a magic-type zanpakuto whose special ability can be summarized as "the power to manipulate dimensional boundaries". What exactly this means is that it gives Himura a variety of abilities including the power to cut along a two-dimensional plane or cut from multiple directions at once with a single blade. They also allow him to teleport over short distances and levitate and control the blades individually. The swords themselves are designed for equal parts mobility and power.

Himura has long since achieved his Bankai, named Koutou Taka (Lit. "Soaring Hawks"). His bankai sacrifices the sword's shape for control over a "dimensional area" in which Himura can levitate objects, fly through the air himself, as well as use both of his cutting abilities with a much larger range by way of the two katana that replace the khopesh pair. His dimensional area has a maximum radius of 500 meters with the center being the point he entered bankai from.

Himura's attire also changes to something between a sort of "royal garb" and a pilot's uniform. It looks like some form of white and gold military uniform with a pilot's hat in place of his signature officer's hat, bearing the crest of a double-headed eagle instead of the medalion symbolizing his clan.

Spirits
Kotori Asobi's two spirits take the form of a pair of blue swallows, flying around in an endless blue sky filled only by clouds. The larger one is male, and the smaller one is female. They are wise but energetic, urging Himura to think about his actions but not to "think too long!"

When they materialize in human form during Muramasa's Zanpakuto Rebellion - and later revealed they can do so at any time - they take the form of a pair of middle-school age children dressed in blue uniforms resembling those of a military academy. The boy wears a blue blazer with gold trim and buttons, as well as blue slacks. The girl wears a similar blazer, though with a ribbon instead of a tie, along with short-shorts and long stockings striped in white and reddish-purple (the same color as the sword wrapping) that reach up into her shorts. Both wear formal footwear in appropriate styles, as well as having blue hair with red bangs. The boy's hair is in a standard formal-Japanese style, and the girl's is longer but similar and tied in a ponytail. Both manifest an energy blade instead of their standard katana form, however their Shikai form remains the same when they use it. Both of them have swallow wings and tails on their back and can fly through the air swiftly and deftly.

Trivia

 * The materialized Kotori Asobi were the first victims of Nero's Tsukuyomi (though he only managed to knock them unconscious with it).
 * When materialized, the boy appears right-handed and the girl left-handed, the same way their respective swords are typically held by Himura.
 * As well, the girl often holds her sword backward, the way Himura often holds her sword.