Zanpakuto

The relationship between zanpkauto and master is unique in the sense that Shion's blade is not occupied by the actual zanpakuto spirit.

Instead, the spirit known as Fuyūrei is simply a cast-off, an empty husk created by Shion’s actual zanpakuto spirit, Hyakki Yagyō, to take its place (similar to, but not exactly like, how Katen created Kyoukotsu to hide the Shinken Hakkyoken).

The “true” zanpakuto spirit is locked in combat with Shion’s inner Hollow, and cannot come when called, hence the need for a “substitute”.

The reason this had to happen is because Shion was unwilling to come to terms with the Hollowfication, and was the last among the Visored to confront their Hollow, by which time it had gotten out of control, forcing the zanpakuto spirit to step in.

Because of this substitution, Shion can’t currently access the full extent of the blade’s abilities. They accept this as punishment for having ignored the situation for so long. Besides, its not much of a detriment as it would be to other shinigami, as Shion still has their kido skills to rely on.

If there ever comes a time when Shion puts on the mask and releases their inner Hollow, then their true zanpakuto spirit will be free to occupy the blade and lend its abilities. Alternatively, if Shion is desperate enough to call upon their true zanpakuto, it means that inevitably, the inner Hollow will come with it, although its risky, as Shion might not be able to get the mask off again.

Before the Hollowfication Incident, when Shion was captain of the Tenth Division and was using their true zanpakuto, they still relied mostly on kido so not many knew its name even back then. So currently, majority within the Soul Society don’t even know about the change.

Fuyūrei, the husk spirit, resembles a massive humanoid creature that has no physical form or defined gender.

Instead, it is composed entirely of coils of cloth that constrict and unravel as it floats, similar to a wrapped corpse. It wears a metal visor across its head with black swirling patterns where its eyes should be, greatly resembling Shion's Hollow mask. Over its head, it wears a dark wide-brimmed straw hat fraying at the edges, with a metal tip and a cord that hangs loose below its chin.

Hyakki Yagyō, the true spirit, resembles a young human of ambiguous gender. The spirit retains their wide-brimmed straw hat and metal visor in this form as well, making it difficult to decipher their facial features. They have a slender, toned body draped in a loose violet yukata with a chokuto resembling the zanpkauto's sealed form secured to their obi. Their feet and hands are bare, only wrapped in fraying bandages.

The spirit is soft-spoken and formal in their mannerisms. Despite being incredibly loyal to Shion, the spirit never fails to call them out when needed. In a lot of ways, Hyakki Yagyō treats their shinigami like a kind but uncompromising parent -- by dealing with their master's bad decisions with patience and tolernce, but making sure they understand their mistake and face the consequences as well (which, in this case, is not being able to access the spirit's true abilities).

S H I K A I

Fuyūrei [浮遊霊 | Wandering Spirit]

When Shikai is invoked with the release command "Arise and Unbuild", the blade takes the form of a long ornate smoking pipe. The pipe continuously absorbs reishi from the surroundings, and 'burns' it at the tip, where the tobacco usually is.

The reishi particles are then converted to reiryoku, which Shion can inhale through the other end of the pipe, replenishing their own spirit energy. As kido spells require continuous use of reiryoku, releasing shikai ensures that Shion wont run out of energy mid-battle.

Due to the circumstances behind Shion's zanpakuto, this is not the true form of the shikai and is purely for support purposes, allowing Shion to amplify their other skills.

T R U E - S H I K A I

Hyakki Yagyō [百鬼夜行 | Night Parade of One Hundred Demons]:

Hyakki Yagyō is the shikai's true name, and its offensive techniques can be accessed only when Shion's true zanpakuto spirit is occupying the zanpakuto.

The blade assumes its true form, which is of a massive smoking pipe that's larger than Shion themselves.

The amount of reishi the pipe can absorb is increased monumentally. Shion can use a portion of this newly acquired energy to create an army of puppets. The puppets are constructs of pure spirit energy, and their number can increase or decrease based off Shion's needs. Each of the puppets is considered one of the zanpakuto's ‘daughter blades’ and operates within a contained field surrounding Shion. The perimeter of this field can also be increased or decreased depending on how Shion wants to use it, but spreading it too thin could reduce effectiveness.

Since each one is created from Shion’s reiatsu, the spirit puppets can mimic them perfectly. Any kido spell they perform when the true shikai is active is bounced between and amplified by the army.

The puppets are also capable of attacking the opponent. Shion can either choose to make many weak puppets and overwhelm their enemy with numbers, or sacrifice quantity for quality by making a few strong puppets that can engage the enemy on equal footing.

B A N K A I

Inner World

The zanpakuto's inner world is filled with tall, dark trees, overgrown beyond reason. There is something eerie about the forest. No matter how bright the sun shines in the outside world, it remains dark and foggy.

It smells like something died. Strange noises fill the rusty air: squeaks and screeches. Somewhere out of sight, you can always hear the dull thunk-thunk-thunk of someone chopping wood. The wind plays soft melodies on ghostlike flutes.

It's easy to be led astray inside it. Best to stay on the path.

At the heart of the forest is a clearing, if you're brave enough to go looking for it. Within it, the true spirit and the inner Hollow are locked in eternal combat. Above and around you, they clash like a frantic melody. You can hear the sounds of their battle, but they are invisible to the eye.