Aether-Thief's Edge

Weapon (Shortsword), Very Rare (Requires Attunement by a Rogue)

A masterfully forged silver shortsword designed to drink in destructive magic. A slender, translucent vein of crystal runs from the pommel up through the center of the blade, waiting patiently to absorb an arcane blast and empower its wielder's next deadly, precise attack.

Enchanted Edge

You gain a +2 bonus to attack and damage rolls made with this magic weapon. If you have the Weapon Mastery feature, you can use the Vex property with this weapon.

Elemental Siphon

The sword has a number of charges equal to your Dexterity modifier (minimum of 1). It regains all expended charges when you finish a Long Rest.

When you are damaged by a spell that deals acid, cold, fire, lightning, or thunder damage, you can use your Reaction and expend 1 charge to absorb the magical energy. You take half damage from the spell. The sword then stores the exact numerical value of the damage prevented (for example, if a spell rolls 100 damage, you take 50, and the sword stores 50).

Upon absorbing this energy, the crystal vein running through the weapon violently flares to life, shedding dim light in a 5-foot radius. The blade glows with a color matching the consumed element—a roaring crimson for fire, a blinding sapphire for lightning, a biting white for cold, a seething emerald for acid, or a deep violet for thunder.

Unleashed Strike

The stored elemental energy from Elemental Siphon lasts for 1 minute or until you hit with an attack.

The next time you hit a creature and qualify for a Sneak Attack using this weapon, the stored energy is discharged. You roll your normal Sneak Attack dice and add the stored number as a flat damage bonus of the absorbed elemental type. Upon landing the strike, the blade's glow fades back to an inert, glassy silver.

Rules Interaction: If you possess the Evasion feature and succeed on a Dexterity saving throw against a spell (taking 0 damage), there is no damage taken to halve and store. To absorb energy, you must be subjected to a spell you fail a save against, or one that uses an attack roll.

Proficiency with a Shortsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Rogue, Finesse, Light, Vex