Mayuri Kurotsuchi

is Captain of the 12th Division in the Gotei 13 and 2nd president of the Shinigami Research Institute. He gained his position after Kisuke Urahara, the former captain and president, was sentenced into exile by Soul Society. His lieutenant is Nemu Kurotsuchi, his "daughter" created artificially by himself.

Personality
Mayuri Kurotsuchi is a researcher and personifies the stereotype of the mad scientist. In the earlier episodes of the anime, he is displayed as one of the most sadistic and cruel characters in the series. He sees everyone and everything not as a living being, but as an object to be researched—including himself. He has little respect or regard for most others, and was even willing to turn his own men (who were not aware of his plans) into human bombs in an attempt to capture Uryū Ishida and Orihime Inoue for experimentation. He also withheld vital information about the Bount from the other shinigami in order to capture one as a research subject for himself.

Appearance
Mayuri's appearance has a very skeletal look to it with a skull-like visage. His fingernails are blue and, with the exception of the fingernail on his right middle finger, are all short. The one long fingernail is as long as the finger itself. In the anime, Mayuri is revealed to have blue hair and yellow eyes when unmasked. He also wears a white hat with two ends that point to his right and a large purple scarf around his neck. It appears his physical modifications become undone each time he reconstitutes himself, although he is heavily scarred and his ears appear to be permanently removed.

Mayuri has performed various experiments on himself, some of which include upgrading certain body parts to function as weapons or giving him otherwise useful abilities.

Extension Arm: His left arm can extend out like a grappling hook

Hidden Kusarigama: he is able to pull part of his ear out to form a scythe attached to a rope-like ligament for use as a kusarigama.

Camouflage: He can also blend into his environment with some sort of covering that flakes away once he reveals himself.

In case he is defeated, Mayuri is able to transform into a liquid blob-like entity, unable to be attacked or attack, by stabbing himself with his zanpakutō. He is later able to reconstitute himself, at which point his wounds are healed. This ability is related to the bankai of his zanpakutō.

Mayuri seems to be ambidextrous, as he wields his zanpakutō in his right hand and his scythe-ear in his left (often simultaneously). In the anime's Bount arc, he briefly wields his zanpakutō left-handed, as well. However since that is a filler we don't know if it is true or not.

Kurotsuchi's last name is one of the few shinigami names in Bleach which uses kanji based on the meaning of the name and not the sound. 'Kurotsuchi' means black soil (kuro - black; tsuchi - soil), as does the kanji (涅). However, the kanji's reading (pronunciation) is ne or so.

History
Little is known about the history of Mayuri, except that he was the only one kept in a cage in the Maggot's Nest and was request by Kisuke Urahara to become vice-captain to the newly thought of Research and Development Institute. Nine years later he became the third seat of the 12th Division. He later succeeded Kisuke Urahara in leading the Research and Development Institute as well as becoming captain of the 12th Division of the Gotei 13. He also experimented on Quincy, including Sōken Ishida, Uryū's master and grandfather, in his studies.

Research and Inventions
Unlike the inventions of Kisuke, those of Mayuri are not as well known yet. However, one major invention is present, which is Mayuri's lieutenant and so-called "daughter," Nemu Kurotsuchi, who is the ultimate result of his gigai and modified soul research. It is implied that Mayuri has done extensive research on modifying bodies, as shown by his own modifications, including the ability to regenerate bodyparts by means of a "regenerative serum" and an extendable arm. Another one of Mayuri's abilities likely achieved scientifically is his ability to meld with the color and texture of the environment. He also creates a simple Bount sensor in the Bount arc of the anime. Though not as powerful as Kisuke's equivalent modsoul versions, it is far more effective once properly calibrated. In an Arrancar arc Shinigami Cup Golden, Kurotsuchi is shown as having the ability to change a zanpakutō's race and gender, and presents a catalog to Hisagi and Renji, resulting in Renji's immediate desire to have his zanpakutō altered.

Zanpakutō
Ashisogi Jizō (疋殺地蔵, Ksitigarbha's Killer Head): Ksitigarbha is a bodhisattva that watches over children and the underworld. In Japan, where he is known as Jizō, he looks rather like a baby dressed as a Buddhist monk; Mayuri's zanpakutō has what looks like a giant baby's head on it. Its hilt is wrapped in cloth, and has several spiky protrusions sticking out right below the blade, which appear to resemble leaves. Unlike most shinigami, his zanpakutō's sheath hangs directly in front of him, instead of to his side as they are commonly worn.


 * Shikai: Ashisogi Jizō's shikai command is (掻き毟れ, kakimushire) "rip". In its shikai, Ashisogi Jizō transforms into a deformed trident with curved, serpentine blades and a guard shaped like a baby's head (as Ksitigarbha is depicted), all mounted on his sword's normal hilt.


 * Shikai Special Ability: The baby's mouth secretes a poisonous vapor in this form. The weapon works like the venom of a spider bite; when an opponent is stabbed by Ashisogi Jizō, it severs the brain signals controlling the neural impulses for movement in the limb's of the victim, regardless of where they were struck. Unlike regular paralysis, the pain receptors and nerve endings are unaffected by the weapon, so the victim can still feel pain, even in a paralyzed limb. During the Bount arc, it is shown that healing the stab wound does not immediately remove the inflicted paralysis.


 * Bankai: Konjiki Ashisogi Jizō (金色疋殺地蔵, Golden Decapitating Doll): returns Mayuri's zanpakutō to its sealed state and produces a giant caterpillar in a red cape with a grotesque baby's head and a silver halo.


 * Bankai Special Ability: The creature breathes a poisonous derivative of Mayuri's blood which is lethal to anyone who breathes it, aside from Mayuri and Nemu. Numerous blades can also extend from its chest, allowing it to run through and skewer opponents. Only Mayuri has a cure for its poison, though Nemu usually carries it around. Mayuri can change the composition of the poison, as well, ensuring that no foolproof antidote can ever be manufactured to cure it, and no immunity developed against it. Mayuri has physically modified Konjiki Ashisogi Jizō itself so that it will self-destruct and return to its sealed state if it were to attack him, implying that it is sentient as well as organic, reminiscent of Captain Retsu Unohana's Minazuki.


 * Mayuri's zanpakutō also has the ability to transform Mayuri into a liquid when he stabs himself with its blade. Doing so doesn't kill him, but instead simply leaves him unable to attack or be attacked, making it an effective escape tool. He reforms after a few days. It's uncertain whether this ability is entirely the product of Ashisogi Jizō, since he specifically relates the ability to himself, not opponents. His various physical modifications may have something to do with the effect.