A girl stumbles into a war she didn't know existed and discovers she's been a weapon all along. The magical girl genre burns itself down and rebuilds as something colder, meaner, about legacy and inherited violence. Granbelm refuses to make you comfortable with the prettiness of its premise, pulling the rug out so many times you stop expecting solid ground.

Mangetsu's ordinary night takes a violent turn when she's pulled into a hidden magical conflict she never knew existed. Nearly a thousand years after seven powerful mages gave their lives to seal away all magic, their seal, Magiaconatus, stages Granbelm: a battle held each month to decide which participant earns the title of Princeps, the one true mage. On a full moon night, the cheerful high school student, who has always wished for something she was good at, lands in an illusory realm where six mages are fighting. Taken for an enemy and attacked, she is saved by Shingetsu Ernesta Fukami and her Armanox, Viola Katze. When Shingetsu is ambushed for protecting her, Mangetsu receives an Armanox of her own, White Lily, and chooses to fight at her new friend's side. GRANBELM blends the magical girl formula with giant robot action and drama.