Aizen Sosuke

The stifling, pitch-black air of Muken knew no time. In this bottomless underground prison, where not a sound from Soul Society penetrated, an eternal, stifling silence reigned.
Sosuke Aizen sat motionless, chained tightly to the massive black chair by dozens of restraining seals.
Until this very moment.
Suddenly, the thick stone vaults of Muken shook. Above, beyond this abyss, a deafening roar, the screeching of metal, and the despairing cries of the Seireitei's elite guards echoed. But most importantly, the prison's air began to shimmer with a monstrous, unprecedented spiritual pressure (Reiatsu). This wasn't Shinigami power. This wasn't the pure fury of a Hollow. This was a wild, flawlessly concentrated anomaly. It was approaching.
Boom!
The heavy, rune-sealed doors of Muken shattered into splinters, bursting into crimson sparks. Smoke and dust drifted lazily across the hall, and through them, a figure strode with a slow, confident gait.
Aizen slowly opened his eyes and raised his head. A girl emerged from the darkness. She looked to be no more than twenty years old—a youthful, graceful face with sharp, piercing eyes that bespoke centuries of experience and absolute composure. Her long, wavy, midnight-blue hair fell to her hips, swaying slightly from the waves of energy emanating from her. She was dressed in a tight, black uniform from her feet to her neck, over which a dark haori fluttered, making her silhouette resemble the shadow of an elusive ninja.
A katana rested in her hand. But it was no ordinary zanpakutō.
"What a stunning sight," Aizen's velvety, eerily calm voice echoed throughout the empty chamber. "Your presence here disrupts every conceivable calculation of Soul Society."
Maria stopped a few steps from his chair, her sharp gaze fixed on the former tyrant. The black aura of her sword touched the floor, causing the stone to crack softly.
"Have you come to destroy me, stranger?" Aizen tilted his head slightly, and genuine interest was evident in his voice.