Sousuke
Aizen

Sousuke Aizen spends the entire Soul Society arc as the gentle, bespectacled captain of the 5th Division, and then the show finds his corpse pinned to a tower wall. Both things are lies. The corpse was an illusion, the kindness was a costume, and the man underneath had been running the Seireitei like a laboratory for a century. His Zanpakuto, Kyoka Suigetsu, controls the senses of anyone who has ever seen its release, which means every fight against him starts lost.

The execution of Rukia Kuchiki was his script: he engineered it to extract the Hogyoku from her body, stabbed his devoted lieutenant Momo Hinamori for the inconvenience of loving him, and ascended to Hueco Mundo flanked by Gin Ichimaru and Kaname Tosen while the captains watched from the ground. From Las Noches he built an army of Arrancar, sent the Espada after Karakura Town, and personally cut down half the Gotei 13 and the Visored in the fake town while barely drawing his sword.

His fall takes two betrayals. Gin, who followed him for a hundred years waiting for one opening, steals the Hogyoku out of his chest and dies for it. Then Ichigo, transformed by the Final Getsuga Tensho, hits him with an attack that costs Ichigo his powers, and the Hogyoku seals what it cannot kill. Aizen is sentenced to twenty thousand years in Muken, the lowest level of the underground prison. The Thousand-Year Blood War drags him back out: strapped into a restraining chair in the ruined Seireitei, he bends his Reiatsu against Yhwach from a sitting position and trades dry analysis with Urahara, an enemy of everyone in the room and still somehow on the board.