Tainted Blood

 In this world, magic is everywhere. Some use magic for good. Others for evil. One such magic user was Kadius Innozor. Kadius was a dark wizard, a necromancer, who used his powers to destroy, kill, and steal. He would often tamper with magic, and sometimes created spells. Then, one day, after murdering a young girl, his hands became tainted red. He had unintentionally created a spell. He found it useful, as it caused extreme pain. When Kadius was slain, the secrets of the spell where lost. Until his castle was rediscovered, and his spell books found. He called his spell "Tainted Blood". When one spills the blood of the innocent, there is a chance that, if their soul was as corrupt and evil, their hands would become permanently tainted with the red of blood. This allows for them to use dark magic as a tool, causing great pain and suffering. Only truly corrupt and evil people can wield tainted blood as a spell.