Buster Sword of Spirit (5e Equipment)

Weapon (Slabsword), Very Rare (requires attunement)

A sword that contains the spirit of the user's attack, and store it for a flurry of strikes later.

On a successful hit, one spirit shard is stored in the weapon. You can store a number of spirit shards equal to your level. As a bonus action, you can expend all stored spirit shards to unleash a flurry of strikes, making a number of attacks with this weapon equal to half the number of spirit shards expended, rounded down(minimum 1). You loose one spirit shard for every ten minutes without making a successful hit against a creature.