Name: Mayu
Manifestation: A beautiful woman with long, black hair, blue eyes and wearing traditional samurai robes. She has long fingernails and constantly wears a stern expression on her face.
Release Phrase: "Cry, Hell."
Family: Darkness
Level: Bankai
Sealed Zanpaktou: Kaiser's zanpaktou looks much like a shinken, a sword used in iaido, especially for high level training. There is no guard of any kind and both the scabbard and hilt of the sword look like a small walking stick when the sword is sheathed.
Shikai: Mayu turns into a wakizashi, which has a more ornate scabbard, a rectangular guard and a more ornate hilt. A small chain is connected to the hilt with a metallic scroll replica on the end of it.
Shikai ability: Mayu allows Kaiser mastery of the Darkness element. He can form a shadowy aura around himself, which confounds those trying to sense his reiatsu, either sensing too low, too high or just out of whack, in general. He can also manipulate his own shadow, which has its own uses.
Bankai: "And the Void shall now fight with me. Bankai!" Kaiser says this to release his Bankai, which transform Mayu into a nodachi, a longer version of the katana. The shadowy form of a woman forms behind Kaiser and wraps its arms around him, its long hair, now reaching Lady Godiva levels of length, waving behind her. Kaiser can quick-draw and use iaido with the nodachi, like his other swords, but to compensate for the length, the scabbard of the sword disappears into black mist when it's being used.
Bankai ability: Along with the increase in the mastery of Darkness element, Kaiser can manipulate other shadows within his vicinity. The shadow woman's embrace also serves a practical purpose, serving as an even stronger version of the Shadow Aura present in the Shikai level. This makes getting a correct reading of Kaiser's reiatsu near-impossible. The nodachi can also remake itself using Darkness, should it ever be broken.
Techniques:
All three can be used at either Shikai or Bankai level. At Bankai level, the blows are more powerful and faster and two of the moves become more complex at Bankai level.
Worm Hole Trickery: Kaiser can manipulate his shadow to grow larger and should they intermingle with other shadows, he can transport himself from one shadow to the next, much like a low-grade teleportation. He can also slice through his shadow and have the slice exit out the other shadow, allowing Kaiser to surprise his opponents. (4 turns usage, 5 turns cooldown)
Darkness Clouds: Kaiser can take a piece of his shadowy aura and fire it at his opponent. If it hits, it'll cloud the senses of the opponent, rendering it difficult for the opponent to hear, see, touch, etc. At Bankai level, the shadow woman fires the projectile. If it hits this time, the darkness clouds and confounds the mind, arguably making the opponent very vulnerable by making them hallucinate or hear noises that aren't really there. However, at Shikai level, the energy that has been used in this way must be replaced if Kaiser wishes to continue using the aura to his full potential. Too much use of this ability and Kaiser's aura disappears and must be regenerated via Kaiser needing to use his energy to regenerate it. At Bankai level, it takes longer for the aura to disappear. This move is also completely ineffective if used more than once on the same enemy. (4 turns usage, 10 turns cooldown)
Belated Pain: Kaiser slices at the air, firing a wave of darkness at an enemy. However, Kaiser can freeze the wave, redirect it ONCE and fire it again. A good technique for the overconfident. The freezing and redirect of the shot requires a lot of focus, concentration and energy to do effectively. At Bankai-Level, Kaiser manipulates his shadow into a giant shadowy circle under the opponent, which is connected to Kaiser. Kaiser then slices multiple times into his shadow, firing multiple shadow waves out of of the shadowy circle and freezing them in place, surrounding the opponent in shadow waves. He then redirects and fires them at once, doing a lot of slicing damage. Again, this requires a lot of focus, concentration and energy to do, not to mention preparation (two posts worth of it). (Shikai level: can be used 5 times in one match, 6 turns cooldown. Bankai level: Once per match)
(I'm not sure about the cooldown periods, but hopefully everything is as it should be.)