AN: Thanks MDM11, Goku275, Nox Zephyrus, and Wadeparker. MDM11, I can't answer your question as that would be a spoiler. I can say, however, that I intend to give a lot of Fairy Tail's members a moment in the spotlight.
Also, while rereading the Alvarez Empire Arc in canon, I realized that they never really explained what happened to most of the defeated but alive Spriggan 12 between their defeats and reappearances after Irene cast Universe One. They just sort of disappeared, which won't be the case in my story (at least, not in most cases).
"This wasn't how I was supposed enter Fairy Tail's guild hall," fumed Ajeel silently. He was currently locked in a cell, with anti-magic cuffs binding his hands and his power. In the event that Ajeel found a way to remove the cuffs, Juvia and Millianna were present to re-capture him. "The other Spriggan are never going to let me live this down."
After being defeated by Erza, the dragon slayers had used their enhanced sense of smell to locate Ajeel and brought him back to the guild hall as a prisoner (with Wendy healing the worst of his injuries). There had been talk about questioning him, but Mavis ultimately dismissed it, correctly predicting that Zeref had anticipated Ajeel's defeat and refrained from telling him any important information.
The Spriggan had been informed of this by Millianna and Juvia upon waking up in the cell. He had initially threatened the Fairies, claiming they didn't understand the strength of the Spriggan 12 (especially its most powerful members) and their emperor. This stopped, however, when they responded that the did with a degree of certainty that stunned Ajeel into silence.
With it clear that his threats were pointless, the Spriggan had been left with not to do but mentally complain. And complain he did, until something else caught his attention.
"Hm?" went Ajeel, as he noticed a young girl with salmon hair peeking at him from the corner of the hallway that led to his cell. Realizing that she had been seen, the girl hid behind the corner. "What was that about?"
"That's my daughter," explained Millianna. "Natsu and I named her Erza after the strongest woman we know—" Ajeel grimaced, remembering his recent defeat at the hands of that woman "—although she usually just goes by Blaze."
"Should you really be letting a little kid get close to a prisoner of war?" questioned Ajeel, baffled by how relaxed his enemies were.
"It's fine," replied Millianna calmly. This made the Spriggan certain that she knew something he didn't. The Fairy's next words only rose more questions, though. "Once she works up the nerve to talk to you… well… I hope you can keep an open mind to what she says."
Unfortunately for Ajeel, that was all Millianna would say on the matter. He wouldn't be getting any answers until Blaze eventually approached him herself.
"News from the east!" exclaimed Warren. With the Alvarez Empire's attack foiled, all of Fairy Tail was currently in the guild hall to hear Warren's update. "They've pretty much wiped out all the guilds in Bosco…"
Shouts of surprise and fear ensued, none of the Fairies expecting an entire nation to be crushed so quickly.
"…but their troops are stopped there. I don't know if it's to take control of Bosca or what. And I've got some good news, too! Enemy forces are still approaching from the north, but the combined forces of Blue Pegasus and Quattro Cerberus are going to meet them! The enemy's also taken the southern harbor town of Hargeon, but Mermaid Heel and Lamia Scale are heading there to liberate the town!"
This was met with cheers. Morale began to improve, although they still wondered if their allies would be enough to defeat the Alvarez forces. Amidst the blend of confidence and doubt, a certain idea inevitably began to form.
"First Master, let's go back them up!" stated Romeo, saying what everyone was thinking.
"Romeo's right!" agreed Jet. "We won't be able to look them in the eye if we let them do all the work!"
"This is the time to switch to attack mode!" added Droy.
"Of course we will!" replied Mavis, already deciding on who to send to each battlefield. "Reinforcements to head north will be: Mirajane, Elfman, Lisanna, Gajeel, Levy, Sting, and Rogue."
The selected Fairies gave cries of affirmation, as did the dragon slayers' Exceed partners (who, it went without saying, would be accompanying and fighting alongside them).
"And reinforcing the southern attack," continued Mavis. "Gray, Yukino, Sorano, Wendy, Romeo, and Laxus."
"I will go too," declared Erza, despite not having fully recovered from her battle with Ajeel. Knowing how strong an injured Erza still was, none of the Fairies tried to stop her.
"With Juvia and Millianna guarding our prisoner, the rest of you — except for Natsu — will be charged with protection of the guild hall," said Mavis. "The possibility of an enemy ambush still exists."
"First Master, what will we do about the eastern and western enemies?" asked Makarov.
"The western forces are moving slowest," answered Mavis. "I would think that these are Zeref's reserve forces, to be committed after the fates of the other three have been decided. At present, the east is where our greatest danger lies. Therefore, it is where we must commit the strongest of our forces. Warren, have you made contact?"
Among the confusion of his guildmates, Warren responded confidently. "Of course I have! This'll be the strongest force in Fiore!"
"Are you giving me some sort of secret mission, First Master?" asked Natsu. After Mavis explained that the remaining three Gods of Ishgar and Jura would be handling the eastern front, the Fairy Tactician had taken Natsu and Happy aside to explain why she hadn't given them orders like the rest of the guild.
"In a matter of speaking," she replied evasively. "But first, I need to ask you something. Can you kill Zeref? Are you prepared physically and are you prepared emotionally?"
Mavis looked Natsu in the eyes, staring so deeply that he felt like she was observing his very soul. She knew that the dragon had expressed confidence in his ability to deal with Zeref, but she had to be completely certain.
"Yes," answered Natsu, not even a hint of doubt or hesitation coming off of him. "He's waging war on our guild… on our families. As much as I want to believe that he could give up his plots and join us… it's clear that there's no chance of that happening. I don't like it, but I can and will kill Zeref."
"We will," corrected Happy. "I'll be right by your side, Natsu. We're partners, after all."
"Good," said Mavis, though she felt sad that it had come to this. "Now, going back to your earlier question, neither of you can tell anyone else about the mission I'm sending you on. If the others knew, they might try to join you or get distracted from their own jobs."
Natsu and Happy nodded, having a good idea of what Mavis was about to ask them to do.
"I need you to go to the western front and cut off the head of the Alvarez Empire's forces… to kill Zeref. I'm certain that he's there, hanging back with two of the Spriggan 12 to observe the war clearly and give out orders."
Mavis sighed, a hint of remorse seeping into her voice as she continued speaking.
"I wish I could send someone else with you two. Unfortunately, doing that would spread us too thin, endangering our forces. We can only hope that Zeref's desire to end his curse is strong enough that he doesn't have those Spriggan fight you alongside him."
"Don't worry," reassured Natsu. "I mean, I'd feel better if I was teaming up with someone like Erza or Gildarts, but Happy and I'll manage by ourselves. Heck, with what I've got packing, I just might be able to handle all three of them at once!"
Mavis and Happy smiled at the dragon's boast. If anybody could stop an immortal Dark Mage, Natsu could.
"Your Majesty, there is an object approaching at incredibly high speed," alerted Invel.
Zeref smiled, recognizing the identity of the object. The only question was whether his little brother had come to try appealing to his forgotten compassion or to make a futile attempt on his life.
"Shall we deal with the interloper?" asked August. The most powerful of the Spriggan 12, Zeref had kept August in reserve so that he could use his copied Spatial Magic to transport the western forces directly to Magnolia Town should the right opportunity show itself.
"No need," dismissed Zeref. The emperor then began walking in the direction of his approaching brother. "He lacks the power to kill me, and I'd rather finish him off myself. It's only right, given that I gave him this second life."
The Dark Mage leisurely strolled toward Natsu, even as the dragon-in-human-form arrived and started smashing his way through Zeref's forces.
"1,112," spoke Zeref when he finally reached his younger brother. The blue Exceed that followed the dragon flew overhead. "Leaving 998,888."
"You got here faster than expected," said Natsu.
"Did you expect me to hesitate before approaching you, or that I would let my troops wear you down first?" thought Zeref as he attempted to discern the dragon's current thought processes. "I was just so eager to say hi, Natsu."
"But now it's time to say bye, Zeref," retorted Natsu. The dragon started to unravel a set of wrappings on his right arm.
Behind Zeref, his soldiers whispered curiously about the name Natsu had used until Invel explained that it was their emperor's true name.
"Invel, August," said Zeref, not turning his gaze from his brother. "I'd like you to retreat a couple of kilometers west with all of our troops."
"You too, Happy," Natsu told his Exceed partner. "Stay back."
"Aye."
As everybody else left the two brothers alone, Natsu addressed Zeref again.
"We're never handing over the First Master."
"The only reason it's come to this is because you could not destroy me."
"Yeah, well that's about to change," retorted Natsu as he finally undid the last of his wrappings. A tattoo of a dragon was exposed, one that radiated pure power to Zeref's sense. "Here I come!"
With that, Natsu's left arm ignited. He swung a flaming fist at Zeref's face and sent the Dark Mage flying backward.
After a collision with a rock formation halted his flight, Zeref retaliated by shooting a concentrated ball of his contradictory curse at the dragon. To the Dark Mage's surprise, his brother destroyed the attack with the swipe of a fire-clad hand.
"He burned the magic itself!?" shouted Zeref in astonishment. But, before he could do anything else, Natsu suddenly appeared in from of him and delivered another flaming punch. And another one. And another.
The Dark Mage was hit over a dozen times before he finally found the opportunity to disrupt the dragon's assault. It took several more blocked attacks before he found an opportunity to speak.
"I'm surprised! What is that power of yours?"
"I got it from Igneel," answered Natsu. "It's the last of his power he left in me. It took me months to be able to release it, and it'll be gone for good once it's used up. It was Igneel's resolve. True Fire Dragon King Mode!"
As the earth around Zeref started to burn, joy began to fill him. His lost hope of finding death's release was restored, and he mentally thanked all of the people who had made this dream possible. Igneel. Anna. Layla. Mavis. And his most beloved, dear brother.
However, Zeref was snapped out of these thoughts when August suddenly appeared between him and Natsu. The dragon was surprised too, which gave the Spriggan the opportunity to grab his arm and teleport the two of them away.
"…I suppose it was too late, anyway," mused Zeref once he recovered from his shock. "I'd already resolved myself to end this world. And now, nothing can stop me. Farewell Natsu…"
Yet, contrary to his words, a single tear ran down the cursed man's cheek.
Omake
"Juvia's probably moping instead of guarding Ajeel right now," thought Gray as he and his fellow Fairies traveled southward. "She wasn't happy about the fact that I was chosen to join the fighting while she had to stay behind at the guild hall."
A wry smile crossed the Ice Mage's face as he imagined Juvia sulking, the image making him feel both happy and concerned.
"Hopefully, she doesn't get so distracted that the Spriggan is able to slip free and hurt her."
Back in the guild hall, a sudden feeling of warmth broke Juvia out of her Gray deficiency-induced slump.
AN: Last chapter, I told Guest that Natsu would be able to show off his strength before the end of this story. When I typed that, I was thinking about this upcoming fight between Natsu and August, which I had already planned before taking a week off. Get ready.
(Hopefully, what I write will live up to this hype. Otherwise, it would just be a bit embarrassing that I wrote the above paragraph.)
Anyway, that's all for now. Bye!