The story of Bleach features one of shonen's greatest villains, the scheming Aizen Sosuke, once the Captain of Squad 5. He presented himself as a charming and benevolent leader, while secretly pursuing forbidden research to create the Hogyoku and gain Hollow powers to exceed his natural limits. He did all this so he could claim the vacant throne of Heaven itself.
At first, Ichigo and his allies thought that Aizen was simply power-hungry and was acting on a god complex. However, startling parallels can be drawn between Aizen and Emperor Palpatine of Star Wars fame, who also claimed the position of ultimate power, but not entirely for his own sake. Both villains were trying to fight off an even greater evil than themselves.
Aizen & Palpatine Used Tyranny To Defend Against Invasion
A fan theory on Quora suggests that Captain Aizen Sosuke knew about the impending invasion from the Wandenreich, the hidden Quincy empire, years before the invasion actually took place. Aizen knew that the passive Soul King and the complacent Soul Reapers were not ready for the events of the "Thousand-Year Blood War" arc, and most likely, he doubted that mere words would convince his fellow Soul Reapers and the Soul King to make adequate preparations.
So, Aizen sought to claim the throne of Heaven by force, and from that position, he could prepare the Soul Society and Heaven itself for what was to come. Aizen acted not for his own sake but for the world, and his cold, calculating methods were the only way to get ready. A small part of Aizen might have even regretted his extreme actions, such as slaughtering Central 46's members and using the ten Espadas against the Soul Reapers, but he had to maintain his facade of wanting to attain godhood. His real goal of defying the Quincy king Yhwach required some personal sacrifices.
This reflects Darth Sidious' own intentions in the Star Wars galaxy in the Legends lore, in the decades leading up to the Yuuzhan Vong invasion in the comics and novels. Sidious already knew of the mysterious Far Outsiders, as did some Republic leaders, but no one was ready for what was to come. So, Sidious formed the brutal and monolithic Empire and stepped up military spending to turn the entire Empire into a fortress that could withstand the Yuuzhan Vong invasion, including recruiting the talented Grand Admiral Thrawn. The Empire was the source of much misery and injustice in the galaxy, but in return, Emperor Palpatine created a galaxy that would at least survive in the face of an even greater threat.
The Fatal Flaw Of Aizen's & Palpatine's Plans
On some levels, Emperor Palpatine and perhaps Captain Aizen were justified in their actions because the enemies they feared were absolutely real. Neither Aizen nor Palpatine made up an enemy to justify their actions -- they were preparing for a tangible threat, and as villains, they resorted to any means necessary to get what they wanted, even if someone else had to suffer for it. Palpatine gladly created a monolithic and tyrannical Empire if it meant replacing the complacent and disjointed Republic before the Yuuzhan Vong invaded, and similarly, Aizen possibly knew that the equally complacent and clueless Soul Reapers would have quickly fallen to the Quincy empire. However, ultimately, Aizen and Palpatine tried to pay too heavy a price for victory.
Even if Palpatine and Aizen had what it took to face the Yuuzhan Vong or Wandenreich, their "fight fire with fire" method sabotaged them, and in hindsight, it was foolish of them to become evil to defeat an even greater evil. Even if they wanted to protect their respective realms, Aizen and Palpatine made themselves targets for their former allies -- the Soul Reapers and citizens of the Star Wars galaxy respectively -- and these villains failed to convince the people that their plans were righteous. Aizen and Palpatine justified their plans in their own minds, but they couldn't convince everyone else of that, so people turned on them and took them down. No one saw the Wandenreich or the Yuuzhan Vong coming, but they certainly saw Aizen and Palpatine and took action to defend what they viewed as the greatest threat to their realms.
In the end, becoming a villain to defeat a villain is sure to backfire, especially when Aizen's and Palpatine's would-be allies were unwilling to take the same villainous steps. No matter how powerful the Yuuzhan Vong or Quincy may be, the Soul Reapers and Star Wars citizens would never allow a known enemy like Aizen or Palpatine to lead them, especially when the impending threat isn't yet known to the common people. Thus, the Soul Reapers and the New Republic had to face these invading armies on their own and hope that dethroning Aizen and Palpatine had been worth it. If not, Aizen and Palpatine would have been vindicated in the annals of history as would-be tyrant heroes.
