Well, yesterday I fought a little about one of Mashima's other works, a good one, but nothing compared to his other works, especially Fairy Tail (By the wat I recommend you to read all of his works: Rave master, Monster Hunter Orage and Monster Soul), Monster Soul.
A little about the series:
The tale of Monster Soul takes place in the land of Elfenland where humans and monsters inhabit. The main characters are a group of monsters called the Black Airs. The Black Airs is recorded as the strongest group of the monster forces in the great war between the humans and monsters.
The first three chapters consist of three stories that do not have a main plot, but the last chapter of the "first stage" reveals a bit of the past.
In the "second stage" the Black Airs travel to Hell to help a human boy save his townspeople who are captured by the evil Tri Command.
Well, here the theory starts
The theory includes only the first stage of the manga because the other one weren't writen by Mashima. I found out some huge similarities between characters from "Black Air" and characters that take part in the Alvarez Empire Arc.
So here's the characters (Biggest simalirity On the top and Smallest in the bottom)
Tooran-A sand golem that manipulates sand and can transform into sand, that is clearly Ajeel.
James-A frankestein, got weapons inside of him and a monster sensor vision, a little spoiler, he is a robot created for hunting monsters. He is Whal with he's weapon creation, weaknesses vision, and he's a robot too, well, a mechias or whatever this is.
Aki-A S-class monster that looks like a human but he can transform into a direwolf, he falls asleep after using his powers. Well, I'n pretty sure he's Wolfheim, he got the word wolf at he's name, and he can transform the resembles Aki's direwolf form, and he's clearly a S-class. So I expect wolfheim to be stronger than we think and have an extremly important role in this arc. After all, Aki is the main character in Monster soul.
Joba-An onion imp. An imp that we all think that will have an huge role in this arc, he's Obra, Obra (or something similiar to him) appears in the shadow picture of the spriggan 12, and after we know there's a relationship between him and Zeref, we know he'll probably return.
Mummy-She's a mummy-woman that can control her bandages, and sh's a hell type. This one is the hardest, she can be Brandish because both of them don't where too much and they have a similiar attitude, but I think she's Dimaria, from the same reasons, and because they look alike.
Is Mashima taking inspiration from Monster Soul here? If he's, this is not the first time.
If my theory is true we probably canfind even more similarities and understand things about the future events in the manga.
Well, I hope you enjoyed reading this post and please comment your opinions about this, especially people that read the Monster Soul manga.