Black Crescent Moon

Dark Yojutsu: Black Crescent Moon (闇妖術『黒三日月』) is a Dark Magic spell.

Description
With an open scroll, the user coats themselves and their sword in darkness and then swings their sword, releasing a wide flying slash of darkness. When boosted by Zetten, the slash is capable of cleanly slicing through the neck of a monstrously large dragon.