When activated, a bright light envelops the area and inflicts massive damage on whoever the caster perceives from their heart as an enemy, leaving friends and bystanders completely unharmed. The choice between friend or foe is decided by the user's heart, and they cannot lie to this Magic. It is considered one of the most powerful Magics and is one of the rare legendary spells, and also one of the three great Fairy Magics.
The Magic's strength was so great that it defeated Jose Porla, a Wizard Saint, in a single blow, during a battle in the Phantom Lord vs Fairy Tail guild war. According to the second master of Fairy Tail, Precht, Fairy Law is a deterrent Magic, meant to discourage further action from enemies, and is not something that should be used lightly.
Setting Law as its basis, Mavis modified and improved it so that users wouldn't suffer from its side effect, but she has noted that this Magic is meant to only be used to a singular target and the more targets the caster uses it on the more lethal it would be to their lifespan, and in the worst cases can cause death to the caster.
- Fairy Tail Manga: Chapter 232, Page 3
- Monthly Fairy Tail: Volume 13 Mashima Hiro-Sensei Long Interview
- Fairy Tail Manga: Chapter 66, Pages 2-5
- Fairy Tail Manga: Chapter 125, Pages 14-16
- Fairy Tail Manga: Chapter 66, Page 4
- Fairy Tail Manga: Chapter 215, Page 17
- Fairy Tail Manga: Chapter 505, Page 10