Sune's Blessed Shield (5e Equipment)
From D&D Wiki
Armor (shield), very rare (Requires Attunement)
A grand silver shield, accented by flowing strands of red and gold. You have a +1 to AC while wielding this shield.
This item has 8 charges. When you are missed by a melee attack, you may use your reaction and a charge to deal radiant damage to them, equal to half your AC, rounded down. This item regains 1d12 charges at dawn.
While attuned to both this item and Sune's Blessed Armor, it does not require a reaction to deal radiant damage to them, but you can only use it once per attack which triggers it.