User blog comment:Crimson and Darkness/Volume 24 discussion blog/@comment-162.252.126.39-20171023222128/@comment-31137559-20171026163541

Armor-type Power of Destruction. It forms into an armor-shape suiting Rias' nature as a Wizard-Power type. And since everyone's getting armor these days. Miyama-Zero might even have an illustration of it. Due to Rias sucking out Issei's dragon aura, she develops the form similar to how Sirzechs developed his True Form.