Ring of the Hunger

Ring, uncommon

This ring slips on your finger, but can't be removed without also drawing blood. As a bonus action while wearing the ring, you can speak its command word to cause it to bite down and deal 1d4 necrotic damage to you, which can't be reduced in any way. For the next minute, the first time you hit a creature with a melee attack each turn, that creature takes an extra 1d4 necrotic damage. Whenever you deal necrotic damage in this way, you also gain the same amount of temporary hit points. When this effect ends, any remaining temporary hit points you have from it are lost. This property of the ring can't be used again until the next dawn.

Curse. This ring is cursed, and using the ring's property extends that curse to you. You remain cursed in this way until you're targeted by the remove curse spell or similar magic. While cursed, you gain the following flaw: "I have an urge to taste blood—even if it's just a little bit—every day. I mustn't let others find out."

They say the first bite's the one you remember the clearest: that rush of iron across your tongue, the warmth against your teeth that leaves you wanting more.
Rest assured that you will spend forever chasing that feeling, again and again, until your world is nothing more than crimson and death.