Law

Law (ロウ Rō) is a type of Magic, a category of Black Caster Magic.

Description
When this Magic is activated, a bright light envelops the area and inflicts heavy damage on the user's target. This Magic is so powerful that it was able to completely counteract the effects of the Tenrou Jade. However, this Magic requires 10 years of training to complete, and it comes with equally risky effects if performed incorrectly or in its incomplete state. When Mavis Vermilion used this on Yuri Dreyar to release him from the evil influence of the Tenrou Jade, this unfinished version not only caused Mavis to collapse shortly after casting it but even stopped her growth entirely, forcing her into permanent youth According to Zeref, she also gained the curse of Ankhseram from using the incomplete Magic, which like himself causes death to those around her that she holds precious and dear to her life.

Eventually, Mavis modified and improved Law by removing its side effect whenever it is used, setting it as the basis for Fairy Law.