Erza and Mirajane visit Crawford, the former Magic Council chairman, and fall into Tartaros's trap. And in exchange for information on Tartaros, Doranbolt frees all the members of Oracion Seis!
That member said Tartaros's power 
comes from curses, not magic!
قال عضو تارتاروس ذاك أنّهم
!يستمدّون قوّتهم من اللّعنات وليس السحر