Isane Kotetsu

is the Captain of the 4th Division and former lieutenant under Captain Retsu Unohana. Her lieutenant is her younger sister, Kiyone Kotetsu, the former 13th Division's 3rd Seat.

Appearance
Isane is a tall, young looking woman with gray eyes and short messy silver hair with strands on the right side of her face that are shoulder-length and styled as two thin braids. She wears a thin dangling red earring on each ear and a standard Shinigami uniform with her lieutenant badge on her left arm.

Nineteen months after Aizen's defeat, Isane's hair is cut shorter and scragglier.

Ten years after Yhwach's defeat, Isane's hair is now straight down and smooth, although she retains the two thin braids she had while previously serving under Unohana's service. As captain, Isane wears a typical white captain haori. Underneath, she now also wears a large white cloth belt similar to Unohana's.

Personality
Isane is generally quiet, shy, and observant, with a strong sense of loyalty. She can be impatient in the face of an enemy, rushing after enemies she has no chance of defeating, including the seemingly unstoppable Sōsuke Aizen. She looks to Unohana as a mentor and mother figure. It is noted by Unohana that Isane suffers from frequent and recurring nightmares, which are often odd or whimsical in their contents. For example, she once had a nightmare involving kamaboko (a fishcake made of pureed surimi), which she intensely dislikes. Also according to Unohana, she rarely talks in a girly manner. Her favorite food, on the other hand, is porridge, to the extent that she is capable of eating it as the three main meals on the same day.

When Isane has time off, she goes to see her sister Kiyone and vice-versa. They are very close sisters who enjoy meeting up and having fun together. Recently, her favorite place to hang out is the Kuchiki estate, in the "secret base of the Shinigami Women's Association". She is a notable member of the latter Association, where her meek nature occasionally gets her in trouble with group activities including getting captured alongside Nemu Kurotsuchi when attempting to take a picture of Byakuya Kuchiki.

Believing that the nutrient level of porridge is very low, Isane started eating porridge when she passed 170 cm in height as she did not want to get any taller. However, she did not stop until reaching 187 cm, her height being another source of frustration for her. Once, after hearing of how sleeping helps children grow, she decides to not sleep again in order to halt her growth. During a meeting of the Shinigami Women's Association, she proposes a Denreishinki sturdy enough to not break if it is dropped from a height of 2 meters, only to be told by Nanao Ise that it is not a common problem.

Soul Society arc
Isane is mostly seen around Retsu Unohana. She is present when Unohana confirms to Sajin Komamura and Kaname Tōsen that Aizen is dead. When Hanatarō Yamada went back to the 4th Division after he met with Jūshirō Ukitake, he gets in trouble with his captain. However, when Isane is walking with him afterwards, Hanatarō asks if what he had done was wrong, and Isane answers he was brave for what he did.

Isane attends the execution of Rukia Kuchiki with her captain on the Sōkyoku Hill as well as her rescue by Ichigo Kurosaki. She appears upset by Genryūsai Shigekuni Yamamoto's false promise to allow Rukia's would-be rescuers to leave safely after her execution, but Unohana tells her that he said it so she could die in peace. After Rukia is handed off to Renji Abarai to get away, Isane hesitantly joins with Chōjirō Sasakibe and Marechiyo Ōmaeda after them. She releases her Zanpakutō to fight against Ichigo Kurosaki, but is taken down, albeit much lighter than the other two. After her defeat, her sister Kiyone runs over to aid her, but Suì-Fēng intercepts her and knocks her to the ground. If not for the fast action of Yoruichi Shihōin, Kiyone would have been killed.

Unohana picks up Isane, and when she starts to apologize for failing to defeat Ichigo, Unohana tells her to calm down. After dropping the wounded off, Isane and Unohana quickly head to Central 46. They arrive at the scene in time to see Aizen defeat Tōshirō Hitsugaya. Captain Unohana announces her presence to the traitors while citing her own suspicions surrounding Aizen's staged death. She also goes on to claim that the Offices of Central 46 Chambers was the only place he could hide and mentions the use of an elaborate corpse doll on his part. Aizen then points out the mistakes in her analysis, while also commending her for seeing through his deception. Isane learns of Sōsuke Aizen's betrayal, and reveals that she and the other lieutenants thought Kyōka Suigetsu was a running water-type Zanpakutō, not one with the ability of perfect hypnosis.

Isane prepares to attack Aizen, but he and Gin Ichimaru quickly get away before she can get near them. Unohana then instructs Isane to use her Kidō skills, both in tracking down Aizen and communicating with the remainder of Soul Society, as well as the Ryoka, on the emergent schemes of the traitorous captain.

After the end of the incident, Isane assists the rest of her squad in healing the wounded. In the middle of the night, she wakes up while having a nightmare about fish paste. She wanders out to get some air while trying to decide what to do, only to be discovered by her captain, who gently tells her to get some sleep. .

Bount arc (anime only)
Note: Events occurring in this arc are only in the anime and do not constitute canon material.

Hueco Mundo arc
Isane arrives in Hueco Mundo with her captain, Hanatarō Yamada, Byakuya Kuchiki, Kenpachi Zaraki, Yachiru Kusajishi, Mayuri Kurotsuchi, and Nemu Kurotsuchi. When Isane and Unohana arrive, they are met by Rudbornn Chelute and the Exequias, who flee after hearing Retsu Unohana is a captain. Isane prepares to chase after them, but Unohana stops her. She and Unohana proceed to heal Yasutora Sado and Gantenbainne Mosqueda. She later tracks down Byakuya's location and does not appear until after his battle with the 7th Espada Zommari Rureaux. She then proceeds to heal Hanatarō and Rukia.

Fake Karakura Town arc
After Mayuri Kurotsuchi announces that he can get Ichigo Kurosaki back to the Human World with a Garganta, Unohana offers to accompany Ichigo back to Karakura Town. Before they leave, she orders Isane to assist Byakuya and the remaining forces in Las Noches. After Aizen is defeated by Ichigo, Isane returns to the Soul Society via Garganta along with Hanatarō, Byakuya and Zaraki.

Zanpakutō Unknown Tales arc (anime only)
Note: Events occurring in this arc are only in the anime and do not constitute canon material.

Beast Swords arc (anime only)
Note: Events occurring in this arc are only in the anime and do not constitute canon material.

Gotei 13 Invading Army arc (anime only)
Note: Events occurring in this arc are only in the anime and do not constitute canon material.

The Thousand-Year Blood War arc
After the release of Genryūsai Shigekuni Yamamoto's Bankai during his battle with Yhwach, Isane notes that her skin had suddenly become dry, to which Unohana remarks that she had said something really girly, greatly embarrassing Isane. Isane stays within the 4th Division's building with Unohana throughout the Wandenreich incursion. After the enemy departs, the rattled Isane begins to question if staying inside was the right thing to do when so many people were dying. Gently berating her, Unohana tells Isane to not act based on her emotions. Breaking into tears, Isane is then reminded that it was the Captain-Commander's last order for them to remain inside. Later, she stands looking out the window, clutching onto a note left to her by Unohana before bursting into tears.

Later, Isane bears witness to the swift and complete invasion of Soul Society by the Wandenreich. The next day, Rukia Kuchiki brings the grievously injured Captain Rōjūrō Ōtoribashi and Captain Kensei Muguruma to her for urgent medical care and Isane sets about healing them. While Isane is healing, Yachiru Kusajishi, who she had enlisted to help her, comes and brings her beds to lay the wounded on. Telling Yachiru to be quieter so they aren't noticed, Isane apologizes for giving her such a dangerous job. When Isane thinks it's a miracle Yachiru hasn't been found considering how loud she is, she is surprised by a voice coming seemingly from nowhere which correctly deduces her thoughts. Trying to locate the voice's origin, Isane is asked where she is looking as Sternritter V, Guenael Lee, appears behind her and grabs her. The Sternritter is punched away by Yachiru, making him disappear. When Yachiru is hit by the Sternritter, Isane runs over to her. She then listens to Guenael introducing himself and his power.

Asking Yachiru what happened to her, Isane is shocked when Guenael appears behind them. Asking if he is a Sternritter, she listens as he confirms this and notes he has already said it before. When Guenael cuts Yachiru, Isane, having forgotten the Quincy, asks why she was suddenly wounded. Guenael proceeds to toy with them, with Yachiru continuously trying to hit him while he vanishes and she forgets all about him between every punch. Isane asks why she keeps punching someone she can't be sure is an enemy and receives a very illogical answer. She then watches as Yachiru draws her sword. Watching Yachiru playing with the creatures manifested by her Shikai, Isane thinks about how unusual the Shikai is. She then sees Guenael rising again and is very surprised when he is cut through the shoulder. She is shocked by the appearance of another Sternritter within the force field she set up to heal the wounded captains. She is confused by Gremmy's claim he created Guenael through his imagination. After watching Guenael's demise at the hands of Gremmy, she demands the Quincy to move away from the wounded, causing him to reveal he's already killed them. She runs to check and discovers the Sternritter's claim to be true.

When Kenpachi Zaraki arrives, Isane asks where Unohana is. She is saddened when she learns of Unohana's death, but is relieved to know that Kenpachi Zaraki has fully inherited her title. She is shocked when Gremmy elevates the ground they stand on. She warns Kenpachi to be careful as she leaves, taking the bodies of Rose and Kensei to safety. Later, Isane goes to Urahara's laboratory, where she assists in the healing of the wounded 11th Division members. When Ukitake claims it was all thanks to her and Hanatarō's work, Isane states that they could not have done it without Ukitake's guidance. After Kenpachi agrees to leave the search for his lieutenant to the rest of the 11th Division, Urahara gives Isane a sphere to charge with her Reiatsu. When the Shinigami reach Wahrwelt, Isane runs through the city alongside several other Shinigami as Lille Barro begins picking off the stragglers.

Ten years after the defeat of Yhwach, Isane has become the 4th Division's captain, with her sister Kiyone serving as her lieutenant. As they attend the promotion ceremony of Rukia Kuchiki to captain of the 13th Division, Isane attempts to take the steam out of a confrontation between Kenpachi Zaraki and Suì-Fēng, prompting Kiyone to tell her not to be subservient to others.

Powers & Abilities
Kidō Expert: Isane is highly proficient in Kidō spells, able to perform high level spells in quick succession for various effects. She has a good understanding of mid- and high-level spells such as '''Bakudō #58. Kakushitsuijaku and Bakudō #77. Tenteikūra'''. Offensively, Isane has used '''Hadō #1. Shō and Hadō #31. Shakkahō'''.
 * As the captain of the 4th Division's, Isane is highly proficient in Kaidō, using it to heal injured Shinigami in the course of her duties.

Expert Healer: As the captain of the 4th Division, Isane excels in healing techniques, being second in the 4th Division only to her former captain Unohana. She is known for speedily providing medical attention.

Shunpo Practitioner: Isane is proficient enough in to keep up with her captain.

Great Spiritual Power: Being a captain of the Gotei 13, Isane boasts a great level of spiritual energy.

Zanpakutō
. In its sealed form, Itegumo takes the form of a katana with a deep blue handle and a pointed round guard, somewhat similar to a snowflake. It is kept sheathed on the left side of Isane's waist.


 * Shikai: Its Shikai command is . When its Shikai is activated, two smaller blades protrude from Itegumo's hilt at 45° angles.


 * Shikai Special Ability: Unknown


 * Bankai: Not Revealed

Trivia

 * "The delicate Lieutenant that does not seem as such from her appearance. She cannot sleep after getting a nightmare. Kamaboko?" - picture caption by Tite Kubo
 * Isane was voted the 32nd most popular character in the third character popularity poll and 37th in the fifth.
 * Itegumo ranked 64th in the first Zanpakutō poll and 32nd in the second.

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