When Aizen ruled Las Noches, there were two prohibitions within it.
First, the Espada were forbidden from releasing King's Flash inside Las Noches.
Second, Espada ranked Fourth or higher were forbidden from using Resurrección beneath the Sky Canopy.
The primary purpose of these two prohibitions was to protect Hueco Mundo's "Sky Canopy."
The sky of Hueco Mundo had no stars, only an endless gray expanse.
After Aizen took control of Hueco Mundo, he found its sky unpleasant and created the Sky Canopy above Las Noches to replace it.
However, no matter how lifelike Aizen Sosuke's craftsmanship was, the Sky Canopy he created had its limits.
Among these, the Espada's "King's Flash" and the Resurrección of Espada ranked Fourth or higher could both damage the Sky Canopy.
The difference was that King's Flash released by Espada below the Fourth needed to be fired toward the sky to damage the Sky Canopy.
But the massive spiritual pressure released when the Fourth Espada used Resurrección could damage the Sky Canopy on its own.
After Aizen Sosuke was imprisoned in Mugen Jigoku, no one maintained the damaged Sky Canopy.
At that moment, beneath the immense spiritual pressure of Ulquiorra's Resurrección, the starry Sky Canopy shattered beneath streaks of black cracks.
Boom!
Blue light flashed, and Kiruge Opie was blasted out of Las Noches by the Lanza del Relámpago Ulquiorra had thrown. It exploded in midair soon afterward.
Rumble!
Perhaps because it exploded in the air, the flames did not form a mushroom cloud. Instead, they violently expanded outward for hundreds of meters like a gigantic fireball.
It looked as though a second sun had appeared in the sky.
Boom!
A powerful shockwave spread outward from the blaze, incinerating everything it struck within its invisible force.
Whoosh!
Ulquiorra, in his Resurrección form, shot out of