Doom's Gate

Key Magic: Doom's Gate (鍵魔法 『』) is a forbidden Key Magic spell.

Description
With an open grimoire, the user sacrifices all of their remaining life span and consumes all of the magic stored by their Key Magic then fuses it into a single gargantuan attack which will then be unleashed on the summoned door. This spell is strong enough to threaten the entirety of Clover Kingdom.