A.N. - Takes place right after Chapter 8, this is considered canon to the story.
Chapter 8 - The Trial Of Fire
The fairy brat completed her trial.
As the world around them began to collapse, Zancrow felt his own existence shifting to another part of the girl's consciousness. Her magic was making it so that he wouldn't disperse, but instead hide it out in a small part of her instead.
It was difficult to explain what his current existence was now. Before, he was just a jumble of memories brought to life by his former guildmate Rustyrose. Then he was possessed by the girl - his new disciple - who somehow kept his memory alive for the Eternal Flame to later revive as a shadow for her to fight.
And now, he was bound to her as some kind of mentor spirit.
"Freaking hell, my life is so weird."
Hearing a voice coming from behind him, Zancrow turned around with black flames already covering his arms. "Who's there?!"
Zancrow found himself looking at a familiar person. "You, you're that enchanter from Fairy Tail."
"Not quite," the boy said. "My name is Arius, and I'm here to make a proposal."
"Arius?" Zancrow gave him a suspicious look. "Yeah, I'm not buying it. You're exactly the same as that fairy brat. The only thing different about you is that you're not bothering to put up that fake personality anymore."
It was easy for him to sniff out that type of person. Even though some would call him a hothead, once upon a time Zancrow was one of the Seven Kin of Purgatory of Grimoire Heart. You didn't get to that kind of position easily without at least learning how to deal with certain kinds of people.
The boy sighed. "If you must know, I'm an exact mental copy of the mage known as Vale. Except my existence is not quite the same as him anymore. Rather, I'm somewhat of a memory like you."
"What do you want?"
"Ah, to business then." The brat smiled. "Now, I believe that neither of us is quite content with our current existence. I believe that there is a way for us to change that."
Zancrow raised an eyebrow. "How so?"
"Enchantment magic," he answered. "By enchanting our personalities onto strong magical objects, I can form us new bodies for us to inhabit. We won't exactly be the same as proper humans, but we'll have our autonomy."
"Is that so." Zancrow sneered. "And what will I have to do in exchange for this 'generous' offer?"
"Merely aid me in the process." The boy standing across from him gestured around them. "Suffice to say, I have no magic power of my own. As a memory barely hanging on to his existence, the only one who has control of our mutual host's magic would be the girl in question… and yourself."
"Me?" And finally, it dawned on him. "Because it used to be my body."
"Yes," Arius nodded. "Even though the total ethernano levels in your body are low at the moment, as a god slayer you can simply recover this amount by feeding on your respective element. In exchange for our freedom, I am seeking you out in aiding me to help recover my magical reserves to use my magic."
"How will I know you won't just stab me in the back once I gather enough magic?"
"You will still have full control of your magic until you transfer it over to me," Arius explained. "I will simply cast an enchantment that will free us both at the same time. If you discover anything suspicious during the process, then you can easily cut the flow of magic power heading towards me during the process. Even if the spell fails, all that would happen is that we would both remain trapped here."
Zancrow hummed. "I'll think about it. Either way, this all depends on whether I get the chance to recover my magic. With the girl still in control of the body, it's not like I have much chances to eat."
"That is merely an opportunity we will have to keep an eye out for."
"But before we agree on anything," Zancrow suddenly interrupted. "I need to ask you something. You, or the brat that you're based on, I recognized something. Tell me, are you actually a part of Tartaros?"
The boy tilted his head in confusion. "No? Why would you think that?"
"Don't underestimate the senses of a god slayer," Zancrow narrowed his eyes. "I could tell the moment I met your original, the two of you are some kind of demon aren't you? You can't be a human, I know that for certain."
Arius's eyes widened in understanding. "Ah, that's a misunderstanding. It's true that we're not human, but we're not a part of Tartaros either."
"That so?" Zancrow looked into his eyes and saw that he wasn't lying. "Huh, you're actually telling the truth. But if you call Zeref your majesty, that only leaves you as a citizen of the Empire."
A demon from the Alverez Empire? As far as he knew, there weren't any such tribes remaining. The only demons that would still exist would be the creations of…
And suddenly, he understood. Without warning, Zancrow burst into laughter as he finally put together the clues.
"Hehehahahah… I knew it!" He wheezed between breaths of laughter. "You're not just a demon, you're a fucking Etherious aren't you?!"
"It's not like Fairy Tail doesn't know it," Arius shrugged his shoulders. "But my original might have termed it as a 'homunculus' instead. Easier to accept than the other term, since the former has a certain connotation to it."
"Hah, a demon infiltrating the lair of fairies. This is the most hilarious thing I've heard in my life." Zancrow grinned. "You know what, fine. As long as you don't screw over my disciple, I'll work with you to help us get ourselves a body. Might as well, since this looks like it's going to be fun."
Zancrow's knowledge of Zeref was spotty at best, most of his information coming from what he learned from Hades. But just from what he learned from his disciple alone, Zancrow knew one thing.
Fairy Tail and Zeref were fated to come to blows. And since Zeref was another being cursed by Ankhseram, then it is highly likely that Zera would eventually meet him at some point. If Zancrow wanted to be able to shake things up by his own actions, then he needed to find a way to get a body so that he could get involved as well.
And there was no way he was going to miss something that exciting.
Originally, this was released before Chapter 9 was in the SB thread version, making this interlude the official confirmation that Vale is an Etherious made by Zeref. Note that Arius will have a bigger role in the sequel story to Enchanted Days.