If Fairy Tail failed to stop Tartaros... what would have happened?

I pronounce E.N.D. as the word "end" and not letter-by-letter because I think it sounds way cooler... also, I don't usually read the manga but when I had this idea for a story, I specially read the Tartaros Arc.

Disclaimer: I don't own Fairy Tail or the cover image but I hope that's what E.N.D. will look like because it's totally badass and I'm pretty sure the big Fairy Tail finale will be Natsu going E.N.D. (what else could it be?)

E.N.D. Rises

Prologue:

Return of the Ultimate Demon

...Unknown amount of time ago...

It was a horrifying sight to watch... Fairy Tail had stood before the members of Tartaros and were crippled by the pain of Face's activation. The magic left Fiore in that instant but before the former mages could recover from their deprivation, Mard Geer opened E.N.D.'s book. The pages flickered as the demonic power was released and the wind swirled around them as things went dark. People got to their feet with the aid of whatever they could grab and Erza weakly lifted her already-present sword. Mard Geer laughed at their pitiful state when a red mist began seeping out of the turning book pages.

"What the heck is that?!" Gray yelled.

"E.N.D.! HE RISES FROM HIS 400 YEAR LONG SLUMBER!" Mard Geer yelled with a smug grin on his face.

The mist cascaded across the floor but avoided making contact with any of the Fairy Tail members. It seemed to be looking for someone... The Demons of Zeref's Books watched in anticipation of where the mist would reform into their guild master. Surprisingly, it didn't. The red mist began to near Natsu when it stopped as if to think. It circled his ankles as if still unsure when it began to close in.

"What the- WHAT IS THIS?!" Natsu yelled but the demons seemed as dumbstruck as him.

"Could it be?" Seilah wondered "Might Igneel have already released E.N.D. so the book merely held his memories and power? But not his actual being?"

The red mist suddenly locked around Natsu's ankles and began to turn black on contact. The pink-haired boy found his feet stuck into place when he tried to move them. His friends attempted to reach him but Tartaros sprang into action and restrained the now powerless mages (some by physically holding them back and others by inflicting curses on them). The mist rose to Natsu's knees as it quickly swirled around him when it suddenly burst into flames!

"NATSU!" Lisanna cried "PLEASE TELL ME E.N.D. ISN'T ABOUT TO USE HIM AS A HOST?!"

The others watched in both horror and amazement as the firestorm encased their friend and blew the roof of off the Cube. There was an ear-piercing scream from Natsu as, for the first time, fire burned him! It left black marks on his arms, up his neck, and across his face. Everything around him blurred as the old memories flooded through his mind and the Demonic Fire Curse filled his (now empty) internal magic container. Natsu fell to his knees as he screamed, the roar of a monster followed close behind.

"NATSU!" Lucy screamed as she suffered on the floor of a painful curse.

All they could see was his silhouette as he fell amidst the raging fire and collapsed to the ground. In an instant, the firestorm dissipated and left Natsu on his hands and knees. Smoke floated off of him as he took deep breaths.

"Natsu...?" Lisanna asked, tears in her eyes.

Natsu pushed himself to his feet to reveal his new appearance. He wore baggy white trousers tucked into black knee-high boots, a black wrap on his left hip with a brown belt, a sleeveless black skin-tight shirt with a grey lining and the Tartaros emblem in grey over his right pectoral, a black elbow-length glove on his right arm with black cloth tied around his wrist, black cloth tied around his left wrist and a black cape fell down his back that was attached by golden clasps. Appose to his clothes, his hair was longer and more rugged and his dark eyes gained an unsettling golden glint in them. The scarf Igneel had given him was left in the dirt at his feet. He stepped forward, at first uneasy on his own two feet, and approached Lisanna as a fanged grin spread across his tanned face. He pinched her chin with his thumb and index finger before whispering into her ear...

"My name... is not Natsu... it's E.N.D.!"

Lisanna gasped and jumped back despite Lamy holding her still. E.N.D. walked away from her with a sadistic smile and he laughed as he looked up to the sky. Fairy Tail looked on in horror as he put his hand over their guild's emblem... and burned it off! Out of the ashes of the Fairy Tail guild mark, the Tartaros guild mark was revealed underneath in grey. It couldn't be true... it couldn't! It had to be E.N.D. possessing Natsu! This couldn't actually be who Natsu truly was! Could it?

"E.N.D.!"

They looked up at the hole in the ceiling to see Zeref standing above them. The Black Wizard looked down at E.N.D. before a genuine smile spread across his face. He jumped down from the ledge and walked over to be standing before the boy once known as Natsu.

"It's been a long time..." Zeref said, almost pleasantly.

"400 years... you couldn't have unlocked me any sooner, Big Brother?" E.N.D. asked him with a smirk "Man... I forgot how great it felt to be me!"

Fairy Tail was stunned. Did... Natsu just refer to Zeref as "Big Brother" or was that E.N.D. talking? Either way, Lucy began to struggle as the curse weakened her. She reached out to him and yelled his name.

"NATSU! Please... snap out of it... E.N.D. can't posses you! You're Natsu Drag-"

Before she could even finish, E.N.D. had his hand around her neck and was lifting her above the floor.

"Don't you get it, yer Blonde Bimbo?! I'm not E.N.D. possessing another's body... I've always been E.N.D.; Etherious Natsu Dragneel!" the ultimate demon told her with a smile at her pain "This is who I truly am! Had that stupid Fire Dragon, Igneel, not sealed my power and memories away, this would have been who I always was!"

With that, E.N.D. lifted her higher into the air and golden-black flames encased his free hand. Lucy looked terrified into his eyes but saw no glimmer of remorse... just psychotic pleasure. He punched her right in her gut and she spat out blood as she flew from his hand. The blonde crashed into Elfman and Mirajane and they all slammed into the wall behind them. E.N.D. laughed at their pain as random red and orange flames began burning from his body.

"Nothing sweeter than another's pain!" he declared "It really is... good to be back..."

He looked back and caught the eye of the horrified Lisanna as she struggled to process what she'd bared witness to. Natsu... was E.N.D., the most powerful of the Demons of Zeref's Books, even stronger than Zeref himself, over 400-years-old and... the man she'd fallen in love with. Unchecked tears ran down her pale cheeks at the sight of the Etherious Demon. E.N.D. walked over to her and pinched her chin again before drawing her face closer to his.

"Hmm... I really did fall in love with you, Lisanna, during my time as a Fairy Tail wizard," he said as he wiped a line of her tears away with the back of his index finger "and it seems... that those feelings still linger,"

He pulled her from Lamy's grip and put his other arm around her waist to keep her held to his side. He moved the hand he had pinched her chin with and caressed her tear-stained cheek with it, holding her face in place. Lisanna looked into his dark eyes in fear when he suddenly leaned down and stole her first kiss. Her eyes widened and his narrowed to look at her. After a moment, he released her and she fell to her knees with her hands over her mouth.

"That... was my first kiss..." she whimpered "I was... saving it for... Natsu... for his birthday..."

E.N.D. snickered at the white-haired beauty.

"Well, I am Natsu and today was the day I was reborn yet again," he said, crouching down to her level "And it was pretty sweet..."

"E.N.D.! Stop playing around with these lowly humans. We've got business to attend to," Zeref said, sounding oddly like an impatient parent.

E.N.D. looked up so him with an irritated expression but got to his feet and joined his brother with the rest of Tartaros in the middle of the room.

"We'll be seeing you, Fairy Tail," E.N.D. said in an almost mocking tone but then the smile dropped and he glared at them with hatred "and then I'll kill every... last... one of you..."

Zeref held his hand skyward with his palm up and his middle and index fingers extended. A black Magic Circle appeared below their feet and a secondary one appeared above them. Powerless, Fairy Tail watched as the emotionless face of E.N.D. - of Natsu - disappeared with the members of Tartaros.

I'm actually pretty proud of this prologue. It's longer than I usually do them, basically a chapter, but it still works the way I need it to.

The scene where Natsu steals Lisanna's first kiss was inspired by the one in Rave Master when Lucia stole Elie's.