Heinley orchestrated the mana decline phenomena to affect the Eastern Empire's mages so he could weaken its strenght and win the war he was planning to start. On that process Evely, a mage of the Eastern Empire and Navier's protegee, lost her magic too. When Navier told Heinrey and he saw how sad she was, he decided to anonymously send her a mana stone necklace so she could regain her powers.
In the future and after being with Navier, she convinced Heinley that the war shouldn't occur and he had to quit his plans, which included retrieving several magic stones that he had placed in the Eastern Empire to make mages lose their powers.
I don't remember why the necklace that is supposed to give Evely's powers back is stealing other mage's powers tho.
Is it cursed? Did sone give it to the magicless girl to steal her magic?? What's going on?