Oh gosh thank you so much!! I'm always happy to know people have seen me through some of my rougher days hahaThe blood pact system is a Jotun thing in my universe, and goes something like this:

The Jotun are a very warrior-like culture, and have little to zero importance on sentimentality, especially mushy stuff like romance. Much more important to them is prowess on the battlefield or in the martial arts, and a Blood Master or Blood Sibling is someone that a Jotun warrior swears their undying loyalty to based on these things.

Jotuns worship a Blood Goddess, so their Priests learn to enchant blood, often giving it magical properties like healing blood potions, or in this situation, enchanting the blood between people. When two (or more) parties agree to become sealed with a Blood Pact, they have a Blood Mage cut corresponding symbols on their palms, enchant the blood of all parties, therefore joining them in a bond that lasts all their lives. Blood Pacts usually give higher empathy between the Siblings, or Master and Servant, granting them slight powers of mental and emotional connection, sometimes even allowing one to give the other magical energy. Common manifestations include: seeing each other in dreams, premonitions involving the other, gut feelings when one is in danger, etc.