Aizen Sosuke

Aizen is a polite, soft-spoken intellectual, often addressing his subordinates by their given names.[13][14][15][16] He rarely shows any sign of alarm or distress, and often has entire situations planned out well in advance. Whenever confronted, Aizen is casual and uncaring, attempting to draw out a conversation and make small talk, which often infuriates those he is talking to.[17][18][19][20]

Aizen initially appeared to be a very kind, well-respected captain and was looked up to by many, especially his lieutenant, Momo Hinamori.[21] However, this was just a mask to disguise his dangerously manipulative nature.[22] In truth, he cares very little for his underlings, and is willing to use almost everyone around him as pawns to achieve his goals. He is willing to stop at nothing to further his ambitions, including manipulating or killing anyone if he deems it necessary.[23][24] He frequently toys with his underlings for amusement.[25][26] Despite any loyalty coming from his subordinates, Aizen proved himself to be uncaring, believing that affection is the furthest from understanding; the one exception to this was Gin Ichimaru, the only person he saw befitting to be his lieutenant.[27] Although he knew from the beginning that Ichimaru wanted to kill him and having taken him under his wing out of curiosity of how he would accomplish it, Aizen would nevertheless be shocked and even saddened when Ichimaru left him to die.[28] During his humble Soul Society years reflected in the Japanese script, his self-referring pronoun used to be "boku", even when conducting his suspicious activities or revealing bits of his true nature. Upon fully defecting to Hueco Mundo, he instead uses "watashi" in a more assertive tone.

During his time as a captain, Aizen liked tofu, but he disliked boiled eggs. In his free time, he often read, and he gave a special lecture of calligraphy at the Shin'ō Academy because he excelled in this branch of arts. This optional course was immensely popular

Aizen is a tall, lean man of light complexion, whose hair and eyes are a similar tone of brown (albeit the latter become more hazel later on in the colored manga). In his original guise as an affable Gotei 13 captain, Aizen kept his hair in a soft, shaggy curtain style and wore black, square-framed glasses, which along with his eyes (slightly droopy at the outer corners) lent him a disarming if not scholarly look. For attire, Aizen donned a standard Shinigami shihakushō with a long-sleeved captain's haori, its inside being a pale turquoise to signify the 5th Division.[3] Over a century ago as a lieutenant, Aizen looked more or less the same as in the present, with the same curtained hair and glasses (but his facial features ever-so-slightly softer); most notable about his attire was the lieutenant's badge around his left arm, with his division's number and insignia upon it.[4]

During his ascent to Hueco Mundo, Aizen shatters his glasses and runs a hand through his hair, revealing sharper, more menacing eyes along with a new hairstyle — slicked back, with a lone strand left to fall into his face.[5] In Hueco Mundo, Aizen initially keeps on a black shihakushō, with a red sash and an Arrancar-style overcoat with narrow sleeves and a standing collar, white on the outside and black on the inside.[6] After Orihime Inoue is taken to Las Noches, Aizen changes into an outfit that is more complete in the Arrancar style, pairing his white coat with a matching undertunic (white with black trim) that in the front, below Aizen's waist, ends with a square cutout. Hakama-like pants remain Aizen's lower wear, also white and black. Contrasting against these is a pink sash (black in the manga) that holds Aizen's Zanpakutō on a silver (golden in the manga) plate. Aizen's new footwear are the typical black Arrancar boots with white lining (meant to resemble the Shinigami's tabi and zōri, but color-inverted).[7] Upon his defeat by Ichigo Kurosaki, all changes that Aizen underwent

Sōsuke Aizen (藍染 惣右介, Aizen Sōsuke) is the former captain of the 5th Division of the Gotei 13, whose lieutenant was Momo Hinamori; before his captaincy, Aizen served as the division's lieutenant under Shinji Hirako.

For over a century, Aizen masqueraded as a benevolent Shinigami officer while secretly plotting his betrayal and conducting depraved experiments, which around 100 years ago led to the Hollowfication of the Visored and their (alongside Kisuke Urahara's) forced exile. Aizen's plans reach a tipping point after he slaughters the Central 46, orchestrates Rukia Kuchiki's execution, and fakes his own death in a successful ploy to obtain Urahara's Hōgyoku. After retrieving said artifact and revealing his treachery, Aizen and his longtime followers, Gin Ichimaru and Kaname Tōsen, retreat from Soul Society into Hueco Mundo, where Aizen is revealed to have built an army of Arrancar.

For his ultimate goal of reaching and overthrowing the Soul King, Aizen uses his forces to wage war against the Gotei 13. After prevailing over most of the Shinigami in his way and achieving a transcendent state through his fusion with the Hōgyoku, Aizen is nonetheless defeated by Ichigo Kurosaki, sealed by Urahara, and later imprisoned in Muken for his crimes. During the Quincy Blood War, Aizen is temporarily freed by Shunsui Kyōraku to help fight against the Quincy King, Yhwach, and plays a pivotal role in the latter's defeat.