As Aizen whispered the release command for Kyoka Suigetsu, the blade emitted a soft whistle and a burst of blue light. This signaled the activation of Kyoka Suigetsu's Shikai (sealed state) ability: Hypnosis. Anyone who sees this blue light falls under Kyoka Suigetsu's thrall.
This Hypnosis manipulates all five senses. A person under its influence can perceive a specific object (including Kyoka Suigetsu itself) differently in terms of its posture, shape, texture, touch, and taste. Imagine seeing flies transformed into dragons or a swamp becoming a field of flowers – that's the power of Kyoka Suigetsu's Hypnosis.
Furthermore, anyone who witnesses the release of Kyoka Suigetsu becomes a permanent captive of its Hypnosis. With each activation, Kyoka Suigetsu can cast the illusion anew.
"Indeed," Aizen murmured, initially satisfied with a slight nod. "Kyoka Suigetsu's Hypnosis requires minimal Reiryoku to activate. However, the subsequent manipulation of the illusion depends on the opponent's strength, potentially draining more Reiatsu." A faint frown creased Aizen's brow as a realization dawned on him.
Kyoka Suigetsu, for all its power, has limitations in its Shikai form. First of all 'Reiatsu Consumption'. Hypnotizing others consumes Reiatsu. If the target is too strong, or if Aizen attempts to maintain the illusion on multiple powerful opponents, he might run out of Reiatsu and be forced to dispel Kyoka Suigetsu's Hypnosis.
Second 'Immunity of the Blind'. Those who are blind are completely unaffected by Kyoka Suigetsu's Hypnosis.
Third 'Limitations of Illusion': Kyoka Suigetsu cannot create something out of thin air. It can only manipulate existing perceptions. Additionally, it cannot alter the sense of "movement and stillness." This means it can't make someone perceive a non-existent object or create the illusion of movement from a stationary object.
(It's important to note that these limitations are established lore from Bleach, not modifications for this story. I verified them on Aizen's entry in a fan-made encyclopedia before writing. These weaknesses sparked my own theories about Kyoka Suigetsu's Bankai form. These theories consider the Shikai limitations, Aizen's usage of Kyoka Suigetsu in the Bleach anime, and the reason why his Bankai was never revealed. However, crafting a Bankai ability that aligns with the established lore and feels logical is quite the challenge.)
For Kyoka Suigetsu's Hypnosis to be most effective in its Shikai form, certain conditions must be met. The anime adaptation of Bleach seemingly contradicts these limitations. We see Captain Aizen effortlessly dispatching opponents and manipulating perceptions in ways that appear to bypass the Shikai weaknesses: the inability to create illusions from nothing and the ineffectiveness on blind targets.
The key to these limitations lies in Aizen's Zanpakuto. In Bleach, Aizen had already achieved Bankai by the time these events unfolded! Yes, the seemingly invincible Kyoka Suigetsu, Aizen wielded was actually its Bankai form. Kyoka Suigetsu's Bankai remarkably addresses the limitations of its Shikai form: The first is eliminating the Shikai's shortcomings of not being able to create illusions from nothing and remaining static.
The second is that the Bankai expands the hypnosis beyond the need for the victim to see the blue light activation. It creates a hypnosis field centered on Kyoka Suigetsu. The range of this field depends on the reiryoku Aizen expends. Anyone within the field becomes a captive of Kyoka Suigetsu's illusions.
Furthermore, Aizen can place this field on specific people, objects, or locations, essentially placing them under a permanent Hypnosis. Examples from the anime include the people Aizen manipulated to deceive Hirako Shinji and the Central 46 members he slaughtered. Undeniably, Aizen's Bankai is incredibly powerful. Especially when combined with the Hogyoku, it allows Aizen to expand the Hypnosis field to encompass the entire Soul Society and even create illusions for the blind. This makes him a formidable opponent.
However, for Aizen specifically, the Hypnosis field of Kyoka Suigetsu's Bankai becomes somewhat redundant. Over his long tenure as a Captain, Aizen had already meticulously placed those he deemed necessary under his Shikai Hypnosis. He even managed to secretly manipulate the only blind person in the Gotei 13th Division, turning them into his subordinates. Therefore, aside from using the Hypnosis field for very specific situations, its overall use for Aizen seems unnecessary.
Bankai eliminates the limitations of Shikai regarding creating illusions from nothing and limitations on movement. However, there's one crucial weakness that persists in both forms: if someone touches the Kyoka Suigetsu, the Hypnosis breaks. This explains why Aizen, in the Bleach anime, never relied solely on Bankai during confrontations. Truthfully, Aizen never truly needed Bankai. He'd meticulously placed key individuals under his Shikai Hypnosis over his captaincy. He even managed to manipulate the sole blind person in the Gotei 13th Division! Aizen's arrogance ultimately contributed to his downfall.
The first reason is Aizen, blinded by his perceived genius and lack of worthy rivals, became somewhat arrogant. Aizen, craving a challenging opponent, deliberately suppressed his own power. This is evident from Captain Kisuke Urahara mentioning Aizen's restraint on the Hogyoku's evolution after a certain event. This implies Aizen weakened himself, and he underestimated Ichigo's potential and the immense power unleashed in the final attack. The resulting injuries hindered his ability to further evolve.
Before Aizen could fully recover and evolve again, Kisuke Urahara intervened and sealed him, preventing his final transformation. Aizen's actions paint a different picture than the image of a calculating mastermind. He craved a worthy opponent so much that he'd deliberately weaken himself. He underestimated his adversary's growth potential. These decisions ultimately led to his defeat...While Kyoka Suigetsu's Shikai has limitations, under the right circumstances, it can still be incredibly effective, just like Aizen's mastery in the anime.
Aizen, confident he can outsmart an unsuspecting Jonin, feels content with Kyoka Suigetsu's Shikai abilities.
It's still early morning. Aizen finishes his daily training and heads straight for the ninja academy. A year has passed since the outbreak of the Second Shinobi World War. Most major ninja villages have concluded their recruitment trials and are focusing on improving their forces for the war effort. This has caused a noticeable decline in the bustling atmosphere of Konohagakure's streets. The war's progression means even children like Aizen in the ninja academy could be forced to serve as expendable soldiers on the front lines. A sense of urgency washes over Aizen as he walks down the school corridor, contemplating this grim reality. Suddenly, a flash of bright red disrupted his thoughts.
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