You gain a +1 bonus to attack and damage rolls made with this magic weapon. The first time you attack with the weapon on each of your turns, you can spend one or more Hit Dice, up to your maximum Hit Dice. For each Hit Die spent in this way, you roll the die and add your Constitution modifier to it. You lose hit points equal to the total, and the target takes extra necrotic damage equal to the total. You can't use this feature of the weapon if you don't have blood. Hit Dice spent using this weapon's feature can't be used to regain hit points during a short rest. You regain spent Hit Dice as normal.