I thought of something and decided to make a proper blog about it, so everyone can decide if my reasoning is possible or rubbish.
The idea I had: perhaps Lumen Histoire is Mavis’ Demonified corpse!
Before you all start questioning my mental sanity, let me give some ideas which may make it possible.
Zeref and Mavis obviously knew eachother, as seen in FT Zero, perhaps Zeref was impressed with her talent for Magic (impressive illusions, ability to use Law) and he may even have fallen in love with her.
Perhaps Zeref’s Curse killed Mavis, and he couldn’t bear to lose another loved one (after losing natsu, his brother) and then he decided to make Mavis into a replacement for END.
Afterall, natsu wasn’t seen or mentioned during FT Zero, so perhaps he was Igneel’s student at the time of FT’s founding. It is possible Zeref doubted if Natsu would be able to fulfill his “destiny” after Igneel tried to destroy him before (maybe Igneel damaged natsu) and decided to make a new ultimate demon, one that could certainly pull it off and he chose mavis.
I noticed that Mavis’ corpse was naked in that crystal, just like Minerva, Mirajane and Natsu when they underwent demonification. If she was stored in there by someone else than zeref, you would think they would at least have the decency to put some clothes on her.
Perhaps Mavis accepted being turned into a new END because she may have realized zeref would someday try to destroy humanity and she wanted to prevent this. So she chose to become the weapon that could kill Zeref.
If Lumen histoire is the ultimate demon then that would explain why some people refer to Lumen as “darkness” and a “weapon”. Of course would the demon capable of even destroying Zeref be a magnificent weapon if someone could obtain it and use it for other purposes (I doubt they would be able to rewrite the instinctive desire to kill Zeref that the demons have, but the seekers of Lumen cant know about this instinct).
Dont forget the western continent, if they are so strong then why would they bother with something that was hidden for so long by a single guild in a faraway continent. They may understand Lumen is one of the three greatest powers in the world, the others being zeref himself and Acnologia or they simply need it to defend themselves from Zeref when he starts his genocide.
Maybe the western continent gave Ivan the information about Lumen and had him search for it, since this would decrease the suspiscion of the council and reduce the danger of etherion being fired on their ass. Ivan may even return in the new story but not as a Shield Spriggar.
Precht may not have touched Lumen when he was master of that dark guild because he knew he couldnt destroy it and that lumen would destroy zeref if he accidently triggered it. If he had told Ivan about it, than Ivan would know where and how to find it.
I think that Zeref wanted to be killed by someone he loved; first option his brother Natsu or second option his lover Mavis. This would cause that the one whose curse kills everything he loves, is killed by the one he loves. I bet Zeref really liked the idea of turning his curse around. Maybe he knew that Mavis would be young forever when she uses Law so he gave her that magic so she will stay young just like him. Happy forever after, that sort of thing.