The story focuses on someone who is Cursed (A person descended from Andirak, who sold his soul in exchange for immeasurable power). Not every descendent can use this power, only every five or six generations are the living who possess this blood able to use it.
However, one catch is that the power is divided by the number of descendants. Andirak originally had 100%. His four children would have had 25% and so on as it passes down. Therefore, the current generation are substantially weaker than the original Andirak. Furthermore, if a Cursed is killed their share of the power is lost, unless they are killed by someone else who is Cursed and they then consume the power.
The plot focuses on someone who realised they are Cursed and desire to destroy the Curse. They are repeatedly hunted by an organisation and she is also unable to control the power. Her journey means that she will have to kill everyone who is Cursed in order to end it once and for all. Including her siblings!