Here's a theory for you

it's about Estelle (ToV) and Marta (ToS2)

basically. They possess the same power. They awaken spirits.

now i'll elaborate of course.
i know apatheia and the cores of the centurions aren't specifically stated to be the same. but what if they are? They do the same thing. And the cores were stated to drive people mad when exposed for a long time. Could be due to leaking aer, could it not?
we don't know if regular summon spirits have such cores and what they would look like, but i think they wouldn't look like the original apatheia.

so, if you agree with the first part, let's move on. because that would mean that Marta would be a child of the full moon as well.
let's check this theory.
Marta can heal and cast spells despite not being and elf or half elf. And we were never given an explanation for either. so it could be the inherent formula that she is born with. or has any of you ever found an explanation? i really couldn't find anything official.
also... Marta is descended of a line of a sylvarant Dynasty, so she even is a princess, go figure.

(and on a different note... Marta and Elle share similarities too.. but I would say that was cooincidence or a slight reference and not foreshadowing...)

so... you agree?