Sōsuke Aizen  

"No, Captain Hirako, your suspicions and vigilance towards me were ideal for my plans. In other words, it wasn't you who chose me - it was I who made you think you chose me, Captain Hirako."

"Cough...cough..." Shinji Hirako coughed up a mouthful of fresh blood. "Aizen, you bastard..."

"Do you understand now, Captain Hirako?" Looking down at the fallen Hirako, Sōsuke Aizen reiterated, "You did not choose me. I chose you."

"Aizen!"

Enraged by Aizen's insult, Hirako's anger peaked. In the next moment, a massive amount of white substance began gushing from his wounds.

However, compared to the others, the white material pouring from Hirako's injuries emerged much more slowly.

Observing Hirako's wounds, Aizen let out an admiring tut. "Captain Hirako, this Hollowfication experiment proceeds faster when the subject's emotions run higher. The others were overwhelmed by the invading Hollow reiatsu, instantly completing their transformations. Yet you, Captain, aware of the truth, can still suppress your Hollowfication's pace. Impressive."

"You scum..." Hearing Aizen's words, Hirako took a deep breath, suppressing his turbulent emotions.

Sure enough, the outpouring of white substance slowed considerably. But it still visibly enveloped Hirako's body at a steady rate.

"In that case, allow me to say a few more things to rile you up, Captain Hirako. How much of that time as your lieutenant do you think I actually spent following you?"

"What?" Hirako raised his head, not understanding Aizen's meaning.

Due to his wariness, Hirako never wanted Aizen out of his sight. Normally, he brought Aizen along wherever he went.

It was only after chatting with Captain Ailin of Squad 11 that Hirako began to trust this man slightly.

"Captain Hirako, my Zanpakutō Kyōka Suigetsu's power is not to cast a mist upon release, confusing friend and foe. It is perfect hypnosis."

"What? Perfect hypnosis, you say?"

"Correct. What an object looks like, the sounds it makes, how it feels to touch, its scent, even its taste... Smell, taste, sight, hearing, touch - these are the five senses humans use to perceive the world.

Kyōka Suigetsu allows me to control and manipulate an opponent's five senses at will, crafting any existence I desire before their eyes."

Making flies appear as soaring dragons, deafening roars like a mosquito's buzz, flesh wounds felt as pierced organs... This ability is what I call - Perfect Hypnosis.

Captain Hirako, because of your distrust, you refused all interaction with me, never letting me leave your sight. So I merely had to make you see someone else following you, disguising them as me. Later, when you began trusting me and opening up, that person nearly slipped.

After all, while I could train them to mimic how I speak and behave around others, explaining my thoughts to you proved...challenging. Thus for decades, I was forced to remain by your side, only able to act at night... Captain, the time I truly followed you amounts to just these past few decades.

Were it not for your diligence all those years, I might have completed this experiment twenty years sooner."

"Damn you!"

Returning his Zanpakutō to its sheath, Aizen continued addressing Hirako. "Captain, perhaps you should apologize to these comrades you've implicated. Being the one I selected, your cherished allies were chosen as my experiments' subjects, reduced to their current state by mere association with you."

"Aizen!"

If Aizen's earlier words allowed Hirako to remain composed, this final insult shattered his restraint.

These people suffered because of him...

With an anguished roar, Hirako instantly leapt at Aizen to attack.

But...

Shick!

Torrents of white substance burst from Hirako's mouth, eyes and ears, rapidly solidifying over his face into a half-mask of bone.

"Such provocation was all I needed to complete your Hollowfication, Captain - one more fruitful result. My gratitude."

"Curse you!" Hirako felt his vision warping, a savage bloodlust rising within.

"No good, my body is accelerating its transformation... That's right, Aizen said emotional spikes hasten Hollowfication. So if I stay calm, the process should slow."

With this realization, Hirako stabilized his emotions before attacking Aizen again.

Clang!

Sadly, his sword never reached its mark – Kaname Tōsen deflected the strike halfway.

Clang! Clang! Clang!

Hirako frantically swung his Zanpakutō, madly assaulting Tōsen until one strike sent him flying.

"This feeling...it's not like I'm the one fighting..."

Though easily defeating Tōsen, Hirako felt no thrill of victory. Instead, doubts clouded his mind.

Normally he would instantly release his Shikai to subdue Aizen's group, not waste time trading blows with Tōsen like this.

"This combat style is more...instinctual. Like a Hollow's..."

"Forgive me, Lord Aizen..." From afar, the battered Tōsen panted heavily, clutching a shoulder wound. "Please, allow me more time. I'll defeat him shortly."

"No need, Kaname. As a research subject, the Captain has performed admirably."

"Captain Hirako, shall we bring this to its conclusion?" Approaching the masked Hirako, Aizen drew his Zanpakutō. "One last thing for you to remember well, Captain... Visible betrayal is easily detected. True terror lies in the betrayals you cannot see coming!"

"Rraaaaghhh!" Hirako let out an inhuman howl, gripping his sword to charge Aizen with both hands.

Shick...

"Impossible..."

As they crossed paths, the lone eye visible beneath Hirako's mask widened in disbelief.

One strike, and Aizen had defeated him?

Hirako's sword never even connected - Aizen's figure shimmered like a mirage before him. Yet a massive wound now gaped across Hirako's own body, inflicted at some unseen moment.

"This is no surprise, Captain." Behind the staggering Hirako, Aizen slowly raised his bloodied sword.

"Once you've witnessed my Zanpakutō's release, it will control your sensory perceptions...forever."

"What??"

Hirako whirled around, glaring at the smirking Aizen. "So all these years while instructing others in Soul Society, forcing them to see Kyōka Suigetsu's Shikai..."

"Correct. Whether intentionally or not, any who witness my Zanpakutō's release will forever have their five senses manipulated by me. Captain, though your actions delayed my research by twenty years, they helped me overcome another significant hurdle.

Currently, every Shinigami in Soul Society is under Kyōka Suigetsu's hypnosis... So thank you for your immense contribution to my studies, Captain Hirako. Farewell!"

As Aizen brought his sword down, a thunderous voice shook the woods.

"Bakudō #4 - Byakurai!"

A blinding bolt of lightning shot towards Aizen with explosive force.

"Oh? More interesting guests, it seems." Rather than strike Hirako, Aizen batted the lightning away with his blade.

Turning towards the forest, the cloaked Kisuke Urahara emerged with the grim-faced Grand Kidō Chief Tessai Tsukabishi. Yet Aizen showed no trace of being caught, calmly greeting them.

"To what do I owe this honor from Captain Urahara and Chief Tessai?"

"Aizen..."

Surveying the fallen captains and lieutenants, their white masks and substances, Urahara's face turned grave.

"You monster...using the Shinigami as Hollowfication experiments..."

"Oh dear, what a mess you've made, Lieutenant Aizen. Shall we eliminate these two as well to preserve your secret?" Hearing Urahara, Gin Ichimaru chuckled slyly at Aizen. "Or make them research subjects too?"

Clang!

Beside them, the wounded Tōsen drew his sword, ready to keep fighting for Aizen's sake.

"Lord Aizen, allow me to kill them."

"No need, Kaname."

"But sir..."