Vampiric Magic

Many magical items, from weapons to door locks to books, created by the Erythraean Empire or the Bloodless Citadel rely on Vampiric Magic. Also known as Blood Magic, items using this technology are/can be keyed to specific individuals' blood to work. This form of attunement is much harder to break and gives the items more power to influence their attuned users, but also requires the users' blood to function (usually proportional to the power).