User blog comment:FairyRaven/Fairy Tail Chapter 421: Wendy and Chelia, Review and Commentary/@comment-4933386-20150223130123/@comment-7418318-20150223130705

Mavis were quite specific about not having used it yet, weren't they?

But if you are right I wonder if Makarov replaced Mavis, or if both of their bodies are caught inside the crystal now (or in seperate crystals).

It'd be interesting if the power of Lumen Histoire grew with each sacrifice, making it even more of a forbidden and two-edged last resort weapon.