Seeing as Mavis is in direct opposition to Zeref, yet they were friends once, I'm starting to see what Lumen Hisotry might really be... which in turn is connected to Mavi's inhuman form. Yep, looks like while Zeref played with turning Magicians into Demons/Etherias, Mavis was playing with turning Magicians into Fairies.
Basing on the Demon's species real name, looks like Zeref's real aim was to remove the threat of death from the society, but since he and that was rejected by the world, it seems he chose to wipe everything out in the end. In a way, Mavis might have also been aiming at it, since her soul is eternally present in the world.
If E.N.D is still sealed, I wonder how he was sealed to begin with, and how and why Igneel couldn't defeat him/her/it.
From the looks of it, just like the other Demons can resurrect endlessly using the laboratory, a similar thing might be with E.N.D., but instead to laboratory, he returns to his Book. Of course that's only a guess basing on what we know.
Also, in those pages above, Zeref suggests that E.N.D. cannot be killed with Dragon Magic, but also suggests that as a Human, Natsu can acquire a different power that might allow him to kill he/she/it.
Also, the decision that Natsu will be faced soon, between "Death" or "Life" in accordance with dealing against E.N.D. might actually refer between the current "life" as is, or "death" and rebirth, or perhaps between becoming a Demon or a Fairy ?
I wonder how Silver will look in his Demon form. Also, Silver having a scar on his forehead in the same place as Gray, but bigger, still leaves the possibility that he might be Future Alternative World Gray (the scars goes in a different direction, but Gray's pretty small, while Silver's wide and deep enough to overlap it). Not to mention Silver seemingly knowing Natsu personally. Also, he has Gildart's vibes :P.
Edit: Of course, I forgot to mention, that it's possible that Igneel was unable to kill E.N.D. because of emotional of reasons... like you know, E.N.D. = Etherias Natsu Dragneel, for example... this would explain Zeref and Silver knowing Natsu to some extend, while Natsu himself not knowing them...
I see your point, Natsu past is still somewhat a mystery. Natsu could be a human child that was born from Dragons themselves. I just wonder how in-depth Hiro will go with the story.
What if END is actually a Demon/Dragon or Demon/Dragon Slayer thats why Igneel couldn't defeat him.
Currently we have quite a lot of Dragon Slayers (3+2+2+1ex), two God Slayers (there were 3 but one died) and one Demon Slayer (Silver is the only known Demon Slayer, as well as the only known member of Tartarus to use Magic, though it seems that he also has a Demon form where he can use curses).
On the other hand, silver did successfully kill a Dragon utilizing the Demon Slaying Magic, so if it was combined with a Dragon Slaying one, I can see it being quite successful even against the higher ranks of Dragons.
Currently, from what we know, the Dragon hierarchy is as follow:
*** Dragon King - attainable by subduing all Dragons:
- currently occupied by the Black Dragon of Apocalypse, Acnologia ?
** Elemental King/Lord - attainable seemingly by subduing all Dragons of certain element (seemingly also simply called as Great Dragons):
- currently only Igneel was confirmed to had attained this rank, as the Flame Dragon King (this means that Natsu is technically a Flame Dragon Prince, thus his father rule over the Fire Dragons should somewhat extend to Natsu, which might be the real reason why dragon controlling magic was broken on Atlas... or thanks to the bond that Atlas shared with Igneel :P),
*Dragons - normal Dragons.
Just what if... it isn't Demon Slayer Magic.... Just a Demon That processed a Dragon instead of a human or Dragon Slayer that doesn't use the typical Dragon Slayer Magic but uses a special Dragon Slayer Curse. What if it was originally a Dragon that Zeref turned into a Human Demon and has Dragon Magic/Curse?
Well look who came back ...Tartaros, E.N.D, Zeref just couldn't resist could you Zero, but tell me the truth it was Wendy that brought you back right lol
Anyways I'm very curious to see what Silver is up to, I get the feeling his a double agent it's just like Zero said he has that Guildarts vibe he seems so similar. I think his gonna be the monkey wrench in this ark.