User blog comment:IamJakuhoRaikoben/Chapter 439: Albareth Empire, Review./@comment-5303512-20150608223123

I think Lumen Histoire is Mavis Vermillion as a almighty living breathing Fairy with OP powers that is capable of doing anything. A prediction somewhere around the final battle, Alvarez's leader will absorb Lumen Histoire into himself becoming an all powerful Fairy. Only Natsu can stop him and he finally learns of his identity as E.N.D. as is somehow able to call upon it's powers and beat Alvarez's leader with Lumen Histoire.

This actually brings me to a Theory about Zeira, I believe that she is not an Illusion Mavis created or a hallucination but a actual Fairy disguised as Zeira. The reason why only Mavis can see her is because Zeira is shy around others so cast some sort of invisibility Spell to anyone but Mavis. Somewhere at the end of the FT0 series, they will have a moment together and Zeira will gift Mavis with the power of Fairies.