Hōgyoku

Known as the Crumbling Orb, the Hōgyoku is a compact sphere of bluish-purple color made from a substance unlike anything else, long thought to erase the boundary that keeps Shinigami and Hollow apart and let one race borrow the strength of the other. Its truer nature runs deeper still, for it perceives the wishes of the people around it and gives those wishes physical form. Two of the orbs once existed, one built by Sōsuke Aizen and another by Kisuke Urahara, until Aizen fused the pair into a single stone.

The orb acts only as a guiding hand. It can bring a desire into being, but solely for those with the raw strength to see it through, and every use wears its power down a little. The trait most feared, the crossing between Shinigami and Hollow, arose because that was Urahara's own wish at its making, letting it drive Hollowfication in Shinigami and turn Hollows into Arrancar. Embedded into a body, the Hōgyoku mends its host's injuries almost at once and, as it comes to grasp that host's heart, reshapes the soul and forces a cascade of transformations. To rouse it from dormancy on demand, Aizen briefly merges it with someone whose reserves at least double a captain's.

Aizen and Urahara are the orb's two makers. Urahara once buried his inside the soul of Rukia Kuchiki to keep it from being found, only for Aizen to defect and pull it back out, then set it within his own chest to remake himself. Many others fall under its reach. Shinji Hirako and his fellow captains become the Visored after it stabilizes their Hollowfication, Wonderweiss Margela is forged into an Arrancar, and Aizen credits it with awakening the powers of Orihime Inoue and Yasutora Sado. In the end the stone refuses the weakened Aizen and restores him to an ordinary state.