Sky-Cutting Sword, A System-Agnostic Magic Item

Sky-Cutting Sword

Description:  A straight-bladed single-edged longsword with a plain crossguard and hilt wrapped in a strange pale blue leather.  When examined under clear skies strange runic writing appears down the length of the blade.  Those able to read arcane languages can read the runes' message as "Let the Skies Bleed!"  Magical senses reveal a very strong aura of elemental and weather manipulation magic.

Powers:  The Sky-Cutting Sword has a potent attack & damage bonus (+4 in D&D terms) against all winged creatures and air elementals.  

Once per day while beneath the open sky, the wielder can spend a full round using the sword to wound the sky itself.  A lightning bolt strikes up from the ground through the user (dealing damage equal to 1d8 x 10% of their maximum hit points, or a near-mortal wound if your system uses wound levels instead) and up the blade, slashing open a gash through which an impossibly dense storm bleeds through.  A torrential downpour begins immediately, and violent winds and thunderstorms rage overhead for 1d6 hours.  The area affected starts at one mile in diameter and doubles each hour thereafter.

Rainfall can exceed 1" per hour, which is likely to cause severe flooding.  Wind speeds can reach or exceed 60 miles per hour.  Depending on the season and natural climate, rain may be accompanied by hail, freezing rain, or snow.  There is a 10% chance of a tornado forming for 1d6 x 10 minutes at some point.  There is also a 10% chance the storm will leave behind whatever bizarre Forteana the GM prefers.    

Possible Origins:  The magic involved in making one of these swords dates back to the Primordial Age when the elements themselves were at war.  Only the greatest artificer would dare to even attempt to make a Sky-Cutting Sword in the current day, and the rituals used are both lengthy (taking at least a year and  a day to complete) and likely to attract supernatural attention from various elemental entities.

Complications:  The most obvious problem is the aftermath of unleashing an uncontrolled and massively disruptive storm that may cause severe damage to the surrounding area.  Using this power in a settlement is likely to be grounds for execution, and that's if you survive the lynch mobs if you've been identified as the cause of the event.

In addition, simply carrying this blade will guarantee extreme hostility from elemental creatures of air, and from most winged creatures who recognize it for what it is.  Creatures associated with other elements my seek to obtain the blade for their own use, or plot to involve the bearer in their own schemes against elemental rivals.  

Using the "wound the sky" power almost guarantees that someone (or something) will take notice and begin seeking the cause.

Design Commentary:  Interestingly, non-elemental creatures that fly without wings aren't affected by the weapon's attack bonuses at all, although that doesn't guarantee they won't take offense at the bearer for other reasons.