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Gran Rey Cero (王虚の閃光, (グラン・レイ・セロ), guran rei sero; ; ; Spanish for "Grand King Zero", Japanese for "Royal Hollow Flash") is an extremely potent higher-level Cero, allowed to be used only by the Espada or former Espada, such as Lucio César.
Gran Rey Cero is performed when an Arrancar draws blood from the Cero firing appendage with their Zanpakutō and mixing their blood with their original Cero. The result is a Cero with a much greater attack power, size, speed, and force, as well as a change of color. This Cero is also many times more powerful than a normal Cero, and is capable of disturbing the fabric of space. When fired, it spins like a razor upon release and compress and decompress, due to the sheer speed and raw power. Unlike most Ceros that mainly take the shape of a sphere created by user and released in a huge blast wave, the Gran Rey Cero, when fired, keeps its sphere form, even after being fired in a huge blast wave. It is a drastically potent Cero and Grimmjow claims that only Espada are allowed to use it.
This Cero is in fact so overwhelming that one of the only two rules the Espada have, according to Ulquiorra Cifer, is that that they must never use it underneath the dome of Las Noches as the sheer force of just using can cause Las Noches to be destroyed.
So far, Grimmjow Jaegerjaquez is the only Espada who has used it before. However, as both he and Ulquiorra called it an Espada's Cero, it is plausible that all of the current Espada are also able to use it. Since Grimmjow is the only one seen to use it, it is unknown if all Gran Rey Ceros are blue in color or if the color is specific to the user.