Bergamot's Blasting Barrier

You target a creature in range. It makes a Dexterity saving throw and, on a failure, is surrounded by a protective but volatile transparent barrier that does not restrict movement or actions. While surrounded by this barrier, when the target is dealt damage by an attack, it takes 1 less damage from the attack and stores 1 + spell level damage. The spell ends when your concentration is broken, you end concentration at any time as a free action, or the duration ends. When the spell ends, it deals force damage to the target equal to the stored damage.

(thanks to my friend Lynch for helping me make this.)