Crack of Thunder (Patreon)

Weapon (longsword), very rare (requires attunement)

While holding this sword, you have resistance to lightning damage. When you hit with an attack using this magic sword, the target takes an extra 1d6 lightning damage.

Energy Surge. Before you make an attack with this weapon, you can cause it to split apart into a group of bladed segments. The segments are suspended in the air and are held together by a powerful electrical force. The reach of your attack is increased by 15 feet, and any target you hit with it takes an extra 2d6 lightning damage from the attack, instead of 1d6. Hit or miss, cracks of thunder erupt from the point of impact. Each creature within 10 feet of the target (other than you) must succeed on a DC 16 Constitution saving throw or take 3d6 thunder damage. If you hit the target with the attack, it makes the saving throw with disadvantage. The weapon then returns to its normal form. This property of the weapon can't be used again until 8 hours have passed or until 10 or more lightning damage is dealt to you (before applying resistance or immunity).

Lightning Rod. Whenever a creature within 40 feet of you takes lightning damage, you can use your reaction to take some or all of that lightning damage instead. When you do, electricity arcs from the other creature to you. You choose how much lightning damage to reduce the triggering effect by; you then take that amount of lightning damage instead.

She was steel and storm incarnate, a cyclone of sword and sparks. Where the mages' bolts tore through the air her blade cleaved them apart, and where they struck her companions that same blade passed a hairsbreadth from their flesh, drawing the brunt back to her only to slash out again with impossible reach.

And with each peal of thunder, another of those usurpers to the power of the sky was cut down by the same power they sought to control, turned back with a swordsmaster's supremacy.