Zanpakutō Spirit

A is the spirit embodying a Shinigami's Zanpakutō that resides within their master's inner world.

Overview
A Zanpakutō Spirit is a part of their Shinigami's soul, and their appearance and abilities are a reflection of this; as such, they also share their master's resolve. They exist in tandem with their master; they are born alongside their Shinigami, and die with them. A Zanpakutō Spirit's power is separate from that of their owner, and when a Shinigami draws on this power in addition to their own, their Zanpakutō will become even stronger. They dwell within the inner worlds of their Shinigami masters.

Appearance
As unique reflections of their masters' souls, Zanpakutō Spirits do not share any common appearance traits. However, a Zanpakutō Spirit's appearance reflects their name and the powers they grant their master. Their appearance can change while their master has their Bankai activated, can be temporarily altered when their master uses a Shin'eiyaku, and varies drastically between spirits:


 * Zangetsu takes the form of his master, Ichigo Kurosaki, but with inverted colors, due to also being Ichigo's inner Hollow.


 * Zabimaru takes the form of a large, white-furred baboon with a snake for a tail.


 * Hyōrinmaru takes the form of an enormous, serpentine ice dragon with large wings.


 * Katen Kyōkotsu takes the form of two separate Human women, due to being a Dual Zanpakutō.

Personality
Though a Zanpakutō Spirit's personality is also influenced by the soul of their master, they possess their own thoughts, feelings, opinions, and desires, which may differ from their master's to varying degrees. Additionally, Zanpakutō Spirits are unwilling to teach their masters new techniques, and will engage them in battle in order to determine whether or not they are worthy. They can also determine if their master is worthy of wielding their power. In some instances, a Zanpakutō Spirit's personality can influence how their master can use their Zanpakutō in battle:


 * Ruri'iro Kujaku's favorite color is azure, and its least favorite color is wisteria. Because of this, Yumichika Ayasegawa, who wishes to hide its true power from others, can release it as instead of as, causing it to sulk and only release a fraction of its full power by becoming a melee-type Shikai.


 * Katen Kyōkotsu refuses to let Shunsui Kyōraku fight at his full power and use the special techniques of his Shikai unless she is in the mood for it.


 * Benihime is described as "not nice" by Kisuke Urahara, who mentions that she would refuse to hold back her power against Ichigo's Zangetsu.


 * Hōzukimaru is very lazy, to the point that it takes Ikkaku Madarame some time to get his Bankai, Ryūmon Hōzukimaru, to full power.


 * Initially, Zabimaru did not fully acknowledge Renji Abarai's power, so when he attained Bankai, Zabimaru gave him a drastically weakened version of his Bankai form called . However, once Ichibē Hyōsube revealed the true name of his Bankai and Renji proved his strength to him, Zabimaru gave Renji access to his true Bankai,.

Communication
Communication with one's Zanpakutō Spirit is essential for a Shinigami's growth. The most common method of communication between a Shinigami and their Zanpakutō Spirit is called, where the Shinigami places their Zanpakutō nearby, enters a meditative state, and merges their mind with that of their Zanpakutō Spirit while entering their inner world. Alternatively, a Shinigami proficient enough in communicating with their Zanpakutō Spirit can do so instantaneously and without any preparations. However, a Zanpakutō Spirit can also pull their master into their inner world or manifest itself in the real world in order to speak with their master.

A lack of communication between a Shinigami and their Zanpakutō Spirit can lead to the power of both being weakened and even prevent a Shinigami from releasing their Zanpakutō. Communication can be lost or prevented for several reasons:


 * Kenpachi Zaraki never heard the voice of his Zanpakutō Spirit because of the mental power limiters he subconsciously placed on himself during his first battle with Retsu Unohana, leading to the power of both him and his Zanpakutō being severely degraded. Additionally, Kenpachi did not even attempt to communicate with his Zanpakutō Spirit because he believed Zanpakutō were simply tools of war that only weaklings fought alongside.


 * Tōshirō Hitsugaya lost the ability to communicate with Hyōrinmaru after Cang Du stole his Bankai with a Medallion.