Blood magic, also known as hemomancy, is a type of magic that involves the use of blood to perform magic but also involves the magical manipulation and control of blood itself.
In a lot of places, this magic is often perceived as dark and forbidden, as it requires the use of blood, either one's own or that of others, in order to cast spells and wield its power. However, in some cultures, hemomancers are seen as powerful healers, using their abilities to cure injuries and ailments that would otherwise be untreatable.
The main difference between these perceptions often has to do where and how the blood is sourced. In some cases, hemomancers may choose to use their own blood, either through self-inflicted wounds or by tapping into their own life force. However, in other cases, hemomancers may choose to use the blood of others in order to cast their spells. Using the blood of unwilling donors, or causing harm in order to obtain it, is generally considered unethical and may be viewed as malevolent or evil. However, there are some hemomancers who are able to use the blood of others in the form of willing donors.
Blood magic is sometimes also used and seen as a way to sacrifice oneself for a greater cause. This could involve using one's own blood or life force to cast powerful spells or achieve a specific goal.
A hemomancer who is facing a powerful enemy may choose to use their own life force to cast a spell that will defeat the enemy, but will also result in their own death. Another may choose to use their blood magic to heal a gravely injured ally, understanding that the process will drain their own life force and ultimately lead to their own demise.
Those who choose to do these kinds of acts may be revered as martyrs and have their sacrifice viewed as a final, ultimate act of devotion or duty, undertaken in order to protect or benefit others.