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

When it comes to the Soul King's organs, one cannot ignore the Wandenreich, where both the Soul King's heart and left arm reside.

"...Aside from what happens to Jūshirō-senpai," Masatsuki Aozaki said, snapping his fingers. "Take some time to keep an eye on Seireitei's shadows."

"Shadows?" Mayuri Kurotsuchi glanced around before turning to Masatsuki. "What do you mean?"

"The Quincy you've been so fixated on," Masatsuki replied with a smile.

"You think that's funny?" Mayuri frowned.

This was Seireitei—the heart of the Shinigami's rule. How could the Quincy possibly be here?

"Nine hundred years ago," Masatsuki continued, as if speaking to himself, "the war between the Shinigami and the Quincy came to an end. But the Quincy didn't perish. In the shadows of Seireitei, they created a hidden space."

"Some of the Quincy who survived the war took refuge there and established a nation—the Wandenreich."

"The war when the Quincy invaded the Soul Society?"

"Exactly."

"But how do you know all this?"