Charge Blade

Weapon Magical, Heavy, Two-Handed Rare (this item requires attunement)

When you make an attack roll and hit an opponent (does not trigger on hitting constructs or structures) the Charge Blade gains a charge, the blade can hold up to 5 charges marked by the runes lighting up on the side.
You can expend charges to gain an extra 1d6 of lightning damage for each charge expended this way, charges must be used before the attack roll is made. If more than 3 charges are expended this way all enemies within 5ft of the target make a DEX saving throw of 15, on a fail they take the additional lightning damage as well.