Bleach: Watch Closely, This Is How You Use a Zanpakutō

A minute later, Masatsuki Aozaki stood frozen in front of the laboratory door. As it slid open, his gaze fell upon a towering, irregularly shaped black sphere, nearly the size of a person.

"This... is Aizen-sama's research?" Masatsuki swallowed hard, unable to conceal the greed in his eyes.

Aizen had always known exactly what kind of person he was.

"That's right," Aizen replied with a calm smile. "This is the result of decades of research."

The lab was silent—no one else was present. The only sound was Aizen's voice, echoing against the sterile walls.

"Decades ago, when I first became the Lieutenant of the 5th Division, my Reiatsu had already reached the first rank of Spirit Power."

"Even so, I never stopped pushing myself. I continued to train relentlessly until, thirty years ago, I reached my current level."

"But I couldn't find joy in it—because from that moment on, the path forward became unclear. No matter how much I trained, my Reiatsu never grew stronger. Even my Zanpakutō, fully released, could no longer elevate my power."

"Eventually, I understood. This is the limit of a Shinigami's existence. Not due to any external restriction, but because of the fundamental nature of what we are."

Masatsuki, already captivated, instinctively asked, "So Aizen-sama intends to break this limitation?"

Aizen's eyes gleamed with subtle approval. Slowly, he spoke: