You must be a Dark Mage to Attune to this item.
You can use 1 Major Action and deal a number of Wounds damage to yourself up to a maximum equal to the Tier of this item and “store” those Wounds in that item. At any time while you are still Attuned to the item and it is in your possession, you can use those stored Wounds to power an ability with the Dark tag, reducing the amount of Wounds damage you would normally take from that use of the ability. This specifically allows you to ignore any text saying that such damage cannot be reduced or prevented, but only with regards to using a Bloodcoral item to do so.
A damaged item fashioned of Bloodcoral automatically repairs itself as if the Mending ritual were cast on it if it has access to fresh blood, and only requires half as many Components to be repaired this way as it normally would, provided that they are all blood-based Components.