"See curses like a Semblance, some people are just made for them. Curses are rare abilities, but also known as Dark Magic"
Curses are a subcategory of spiritual and magical arts that originated from the country of Gusteko.
The most notable traits about curses is they cannot be defend against once activated and they are most effective class of magic when comes to killing. However physical contract between the caster and target are mandatory for curse to work. Furthermore unlike mana-based magic, Curses are only limited to taking lives and have no other application in society beyond that. This caused the practice to become taboo leading it to fall out of favor among mainstream Magicians. Incidentally there are Demon Beasts who are capable of inflicting curse spells through their bites and stealing mana of the victim.