So Erza's part dragon? Still not confirmed, we don't know the nature of Eileen and Belserion's relationship, maybe Eileen as an act of respect and had Erza with a human, still if the case, it would explain so much, because dragons in this series are just stronger and better than everyone, so if Erza is half dragon she has quite an advantage over all non dragons.
I don't know how Eileen invented dragon slaying, but I am sure it will be explained. Though I want to know how she survived those 400 years, was she there when the dragon slayers went to the future, did she go with them. I can't imagine Anna and Layla being able to do the Eclipse spell twice.
Well more of Natsu dreams, and still waiting for Lucy to show up in that dream, speaking of which another NatLu.
The chapter just when things are starting to get good, so 6 of our protagonist they are from 400 years ago, they are all older than Mavis, though if Erza was born after the time jump, than she wouldn't be, so I guess Freed's ruins don't consider a womb alive.
Can't wait for the next chapter.