Breath of Seiryū

You breathe the essence of Seiryu into one willing creature within range, imbuing it with the power to spew magical energy from its mouth, provided it has one. Until the spell ends, the creature can use an action to exhale a necrotic blast in a 15-foot cone. Each creature in that area must make a Dexterity saving throw, taking 3d6 necrotic damage on a failed save, or half as much damage on a successful one. The damage increases to 4d6 at 11th level, and 5d6 at 16th level. After you use your breath weapon, you can’t use it again until you complete a short or long rest.