Aizen Sosuke

Before his departure from the Soul Society, Aizen appeared to be a calm, intelligent man. He had brown hair, soft brown eyes, and rectangular glasses. He wore a haori over the standard Shinigami uniform. During his escape to Weco Mundo, he broke his glasses and slicked his hair back. One strand fell over his face. In Uekō Mondo, Aizen wears Arrancar clothing over his Shinigami uniform.

Aizen is a surprisingly polite intellectual with a seductive voice. He often addresses his subordinates by name. He rarely expresses anxiety or pain. He often succeeds in carrying out his complex plans. Entering battle, Aizen behaves relaxed and carefree, trying to strike up a small conversation with the opponent, which often drives the latter out of their wits. In his own words, Aizen is not bound by any laws of morality or ethics, as he considers them nothing more than obstacles to the realization of his potential. He stops at nothing, manipulates people, and, if necessary, kills them to fulfill his ambitions. He often plays with his subordinates for amusement. As commander of his army of Arrancars, Aizen controls his subordinates, inspiring either respect or fear. Despite Aizen's cold-bloodedness, lack of compassion and moral norms, deep down he felt lonely and longed for someone in this world who could understand and appreciate him. All this time, Aizen tried to find someone who could recognize his talent and strength, but he never succeeded. Countless searches only led to the fact that he, having lost any faith in the possibility of not being alone, decided to hide this dream from everyone and dedicate himself to achieving higher goals, sparing nothing and no one.

Aizen is a highly skilled swordsman, his skill complemented by his immense strength. He can deliver extremely powerful and precise blows, capable of cutting through very strong targets. Aizen is so fast that opponents usually can't tell if they've been attacked by him until it's already happened. He possesses vast experience using Kidō spells. He is well-versed in various types of Kidō and is skilled enough to use even high-level Kidō without using their spells. Perhaps Aizen's most terrifying characteristic is his immense intellect. He is well-versed in the history, strategy, and tactics of the Soul Society, and he has access to knowledge unknown to many. Even by captain's standards, he possesses a tremendous amount of spiritual strength.

Reatsu is the physical force/pressure created by a person's spiritual energy when it is released.

A Zanpakutō is a reflection of its owner's strength and soul, possessing its own personality and will. It is the main weapon of a Shinigami, and the power and abilities of each blade are unique.

Shikai is the second form available to a zanpakutō, and to activate it, a shinigami must be able to communicate with the spirit of their weapon and learn its true name.

Bokai is the final form of a Shinigami's weapon, mastery of which is sufficient to become a formal candidate for captain in Gotei 13. To achieve Bokai, the owner must be able to materialize the spirit of their Zanpakuto in the material world and subdue it.

Gotei 13 is the main military organization of the Soul Society, where almost all graduates of the Soul Arts Academy end up. The main functions of the Gotei are to protect Seireitei from invasion and to escort the souls of the deceased to the Soul Society.

In Gotee 13, as in any army, there is a table of ranks. There are a total of 21 ranks: captain, lieutenant, officers from third to twentieth, and private. The ranks follow a numerical order: the lower the number, the higher the rank. The most important person in Gotei 13 is the Commander-in-Chief. Then come the 13 captains, followed by their lieutenants, then the officers, and finally, at the very bottom, the ordinary Shinigami rank-and-file.

Quincy are spiritually-aware humans capable of absorbing and weaponizing spiritual particles. They are human mediums with the ability to detect the existence of Hollows. It all began when they started training to fight Hollows, to defeat them, just like the Shinigami. The Shinigami wiped out most of the Quincy two hundred years ago to prevent the end of the world.

Arrancars are Hollows who have shed their masks and gained powers similar to those of the Shinigami.

Hueco Mundo is a dimension inhabited by Hollows and Arrancars. It is located between the world of the living and Soul Society. The landscape of Hueco Mundo is a vast, white desert strewn with boulders and numerous sand dunes.

Sousuke was born with unique hypnotic abilities. His spiritual sword is named Kyōka Suigetsu. Only after becoming captain did he gather all the Shinigami of the Soul Society to demonstrate his sword's abilities. Activating his shinigami powers, he hypnotized all thirteen squads, including the captains. Through deception, he convinced everyone that his sword's ability was to create a fog that blinds and confuses the enemy with its reflections, causing large groups to kill each other and allowing the sword's wielder to strike while the opponent is bewildered.

Before becoming captain, he was the lieutenant of the Fifth Squad under Shinsui Hirako. Captain Hirako was the only Shinigami who always suspected Sosuke. According to his own words, Shinsui kept him as lieutenant only to keep an eye on him. Around the same time, Sosuke began secretly experimenting with the souls of Shinigami and Hollows. He transformed himself and several other captains and lieutenants of the 13th Guard Squad into Wizenards (Shinigami capable of using Hollow abilities), destroyed the evidence, and falsely accused Kiske Urahara, who was then the captain of the Twelfth Squad, thus causing the latter's expulsion from the Soul Society.

His true goal is to attain ultimate power by merging his body with Hogyoku and overthrowing the Soul King to take his place and rule the Shinigami and humans himself. He faked his own death and then defected from the Soul Society to Uecomondo along with his two followers, Kaname Tousen and Gin Ichimaru.