This is a stupid and crazy theory, but maybe somebody think similar.
So, in a one hand we have Zeref and Mavis, (this is the part more crazy of my theory). Could be Lucy descendant of they two? We don’t know nothing about Mavis fathers, or even could be Layla their grandaughter?
This is crazy because all can see that Mavis is a child, for that, I think that is more probably that Layla and Lucy will be descendant for Zeref than Zeref and Mavis.
My reason to believe that Lucy could be a descendant or familiar to Mavis is that they are similar. (But this can be the design)
But my theory start here:
- The first we learned about Lucy was that she is a stellar spirit mage like her mom. And we know too that she died in x777.
- Lucy can force the close the doors of spirits and the first time that the spirit king appear was when Lucy said that she was going to change the spirits world’s rules. And Lucy invoked all her spirits in that moment.
- Layla retired from the magic at a young age ( according to Capricorn 20 years before the time skip). But she spoke about the one magic to Lucy.
- We have the case that the project eclipse used stellar spirit magic. But, It was Zeref who built this, why he used that magic? He could used that magic too or someone helped him?
- And Yukino wanted to give her keys to Lucy. What makes Lucy so special?
- Then, we have that Zeref and Lucy have never seen, Mashima notes and the words that Zeref said to Natsu.
- And a lot of details more. She’s very clever, loyal, powerfull (she can resist very potent attacks), she recover her magic quickly, she’s very similar to her mum (they seems clones), the spirit king invited her to the spirit world and considers her as a friend (he gives her aquarius magic too)
So, we can see that stellar spirit magic is important in Zeref’s magic, Layla dies very young, the dragons (BIG SPOILER IF YOU DON’T READ THE MANGA) were spirits inside of dragon slayers. Lucy’s mum knew a lot of secrets (“the one magic”). Could Lucy’s mum knew everything and help the spirits dragons to be inside the dragon slayers? Or maybe she died trying to save Lucy to something?
- And the last, but not less important. Lucy was the only one who escaped from Alegria.!!
With all of this, my theory is that Layla knew something about the future and about Lucy’s power. I thing that Lucy is the bearer of the one magic (as Elie with the Ethelion) and Layla tried to protect her daugther, for that reason, she became ill and died. Maybe she contacted with the dragons and with her lass forces, she helped the dragons too.
With Lucy and Natsu’s powers (unison raid) Zeref could be destroyed, (Acnologia is for Natsu).
But we have the threat of Zeref to Natsu. Zeref will meet Lucy? Maybe he will recognize Lucy or something will happen? Maybe Zeref will try to use Lucy’s powers for his plans?
This is my theory about Layla mistery and Lucy’s magic.