Bleach: The DiamondDust Rebellion - Mou Hitotsu no Hyourinmaru

When an artifact known as the "King's Seal" is stolen during transport from Soul Society, Hitsugaya Toushirou is assigned to retrieve it.

Toushirou goes missing after a battle with the thieves, leading Seireitei to suspect him of treachery.

They order his immediate capture and execution.

Unwilling to believe him capable of such a crime, Ichigo, Rangiku, Rukia, and Renji set out to find Toushirou and clear his name.

Meanwhile, Toushirou is still searching for the thieves, and stumbles upon a dark secret involving a shinigami long since dead.