"It seems you've found your answer," he said. "Then let us begin your real training."
[Pure Soul Court · Technology Development Bureau Underground Training Ground]
Sasuke stood in the center of the empty training ground, surrounded by transparent barriers of spiritual energy. Aizen stood outside the barriers, leisurely leafing through a book.
"Are you ready?" Aizen asked without looking up.
Sasuke didn't answer. He simply drew Ame no Habakiri. Its blade gleamed bluish-white under the lights, and black lines could faintly be seen flowing within the fine cracks along it.
"Your eye power increased dramatically after your Mangekyō Sharingan awakened, but that isn't enough." Aizen closed his book. "The Mangekyō's true power lies in its resonance with your Zanpakuto. Only when your eyes and blade become one can you unleash your true strength."
"Become one?" Sasuke frowned.
"Yes." Aizen entered the training ground and stopped before Sasuke. "The Mangekyō Sharingan reflects the mind, while a Zanpakuto extends the soul. When the two synchronize, your power undergoes a fundamental transformation. That is what we call 'Mangekyō Liberation.'"
He extended a hand, gathering a mass of blue reiatsu at his fingertips. "Try looking at my reiatsu with your eyes."
Sasuke activated his Mangekyō, the three-bladed shuriken patterns spinning in his eyes. Through them, he saw that Aizen's reiatsu was no longer simply blue. Instead, it revealed a complex, layered structure-the outer layer was a false appearance, the inner layer its true essence, and in its deepest reaches lurked something he couldn't see through.
"What do you see?" Aizen asked.
"Falsehood and truth... and something I can't see through."
"Good." Aizen nodded approvingly. "The Mangekyō can see the essence of things, but even it has limitations when faced with higher powers. That is the obstacle you must overcome."
He withdrew his hand. "Now,