Sacrificial Blood

Header Artist - David Romero - Artstation.com

Magic:

All magic is the property of the spirit realm. Users must open a passage between the spirit realm and our realm to harness the magic within.
NOT ALL MAGIC IS CREATED EQUAL
Magic use in our realm is a spectrum of strength. The creatures of the world are all born with differing levels of innate relationships to the spirit realm. The faefolk(Alfir, Teva, Eldblud, and Foukka) are the nearest to the spirit realm as that is their ancestral home, making magic use far more common and more powerful. The humans of the world are the furthest from the spirit realm, as they were wholly developed in this realm, causing the use of magic to be very rare, and often weak. Many of the other creatures of the world also use magic, the sapient species use it intentionally in much the same way as the humans and the faefolk, the non sapient species use it instinctively and often defensively. The relationship between the creatures of our realm, and the spirit realm is the main factor in magic use in our realm. Magic resides in the spirit realm, and for any creature to use it, they must open a passage to the spirit realm, and act as a conduit through which the magic can be directed and used.

Methods of Accessing the Magic of the Spirit Realm.

Emotional connection - deep emotional connection to the spirit realm is what allows the faefolk and non sapient creatures of our realm to connect to the magic of the spirit realm. This can be achieved by humans as well, however the connection is difficult to earn, often lifetime devotions to spiritual pursuits of meditating, rituals, and practices. This is extremely difficult for humans to achieve, and often they become hermits in the process.
Sacrifice is the surest way to open a passage into the spirit realm. Regardless of your emotional relationship to the spirit realm, gifts of sacrifice are the most common way of opening a passage. The value of the sacrifice is congruent to the value of the magic gifted in return. Simple sacrifices, only bring forth simple magics. Difficult sacrifices, pay for strong magics, and sacrifices of blood bring the most powerful magics.
Sometimes a passage opens from the spirit realm spontaneously, and creatures come through into our realm. These creatures retain their innate ability to use magic, and can inhabit these lands long enough to form a population. This is believed to be divine in nature, from the guardians of the spirit realm themselves, it is unclear if the guardians are the gods that are worshiped across the lands, or if the gods are feeble attempts at explaining the guardians, by minds incapable of understanding the truth.

Power of Sacrifice:

Access to the spirit realm is most often earned by the power of sacrifice.   Sacrifice must always negatively affect the sacrificer, this is known.    It can be simple, gifts of food and drink are enough to open superficial passages to the spirit realm.
The most powerful sacrifice is blood sacrifice.  The sacrifice of ones essence is the most honored of all gifts.    The gift is blessed, and the blood, once sacrificed is changed, sanctified by the guardians of the spirit realm.

Sanctified Sacrificial Blood:

Like everything else, all Sacrificial Blood is not created equal.  Sacrificial blood can either be willingly sacrificed, or unwillingly sacrificed.   The difference between the two is murky, if a person sacrificed one of their animals, the sacrifice is unwillingly sacrificed, by the animal, whose life is dependent upon that blood.   The only blood that is willingly sacrificed is that of the sacrificers themselves.

Black Market Trade:

Where there is a commodity of value, there grows a market.  The sacrifice of often means the loss of life, and thus a taboo of acquiring the blood arose.    If a practitioner wishes to become powerful and utilize strong magics, they will require ample amounts of Sacrificial Blood.    
Enterprising merchants have begun to fill the opening in the market. The source of the blood is never questioned, but the merchants categorize the blood into grades.  Willingly given blood fetches a much higher price than the unwillingly sacrificed blood is much cheaper, however this blood is much more common.
Willingly sacrificed blood fetches a blood premium, because of its rarity.  The only way to get it is to harvest and collect the blood of someone who does it to themselves.    It has been said, that if one knows where to go, they can sell themselves to a merchant, who takes their blood and pays the family of the sacrifice.   It has become a way for impoverished families to raise their station.
In Valsgard, where magic is exceptionally rare among humans, the magic users are the most powerful.  This power brings with it hatred and scorn due to the taboo of blood sacrifice among the Valsgardi.  The practitioners of magic are forced to keep their work secret, for if it were known, they would be forced out of society.

Type

Biomaterial