The island at the center of the lake had been swallowed by bloodred light. Muramasa's body warped, and masses of black-and-crimson spiritual pressure burst from him, transforming into Gillian-class Great Hollows.
Fear gripped everyone. "What the hell are those?!"
Crimson ripples spread across the lake, staining its waters red.
Yuko watched Muramasa at the heart of the crimson glow. "Without their masters as a source of power, even the strongest Zanpakuto will vanish once their strength runs out."
"A Zanpakuto and its Soul Reaper are one. It survives by sharing its master's soul." Rukia clenched her fists, sadness in her eyes. "In other words, to maintain a physical form, it needs another source of power to replace its Soul Reaper master."
"That must be why he devoured Hollows."
Yuko nodded slightly. "Muramasa can maintain his physical form not just because he's taken enough spiritual power from Hollows, but because of his own unique nature."
"Even without Hollows, absorbing Reishi from the air could sustain him for a long time."
In other words, his ability to operate independently was at least A-rank. Even without a master, he could remain physically manifested in reality almost indefinitely, provided he had enough power.
But the Reishi he could draw from the air wasn't enough to sustain his activity forever. That was why he had been forced to hunt down Hollows and devour them.
Put simply, the spiritual energy in the air was like scraps floating past. It could hardly fill him up.
"How could this happen..." Orihime knitted her brows and tugged at Yuko's sleeve. "Teacher, help him."
"...It's no use." Yuko shook her head. "It sounds harsh, but a Zanpakuto is an extension of a Soul Reaper's soul. It depends on that Soul Reaper, and exists for their sake."
"It's like a relationship.