Author's Note: Hello! Here's a one-shot I wrote based on this prompt: Natsu is a demon summoned by wizard Gray to do their bidding.

This fic was also Kuroshitsuji - otherwise known as Black Butler - inspired, so it will obviously carry some elements from that manga.

Okay, just a warning: Some of what I wrote might not make sense. At all. I am sorry for that. I am also sorry if I managed to mess up Gray's state of mind and character - which I know I did - or if I managed to botch the demon summoning elements as well. Or even END's character. ... Sorry.

So, if Gray seems super OOC, then please keep in mind that he's feeling a bunch of emotions. Remorse, anger, ruefulness, fury, immense sadness, regret, extreme animosity, and so on. He's trying to summon a demon, for goodness sake, and has to appear composed. And even though I am incapable of writing END as a super scary fire demon, he still appears like that to Gray, whose life was destroyed by a demon and who hates fire and even fears it, a little. So yeah.

Disclaimer: I do not own Fairy Tail; my name is not Hiro Mashima. I do not own Black Butler either, nor do I own ideas from that manga. The conditions are Kuroshitsuji based; based on Ciel's conditions for Sebastian (not completely the same though). However, the poem/rhyming thing I wrote for the summoning is of my own creation.

"This is what Gray's lines look like." (with the exception of the chant)

"This is END's lines."

This is thoughts.

Without further ado...

Deals with the Devil (aka a Demon Called END)

The sun was setting over the icy mountain peaks of the Hakobe mountain range. Harsh winter winds whipped fallen snow around, creating the effects of a fierce winter blizzard. Up here, deep in a region where no man dared tread, it was world of darkness falling over a snow-white backdrop as the dying light of day faded away.

Gray pulled the curtains across his windows, shutting away his view to the snow flurry outside. He didn't need any distractions. He checked the door, ensuring that it was properly locked and secured before checking his other windows. When all was to his satisfaction, he slowly walked about the room, extinguishing the fire lacrima. His steps were unsteady, his heartbeat ringing in his ears with thought of the taboo he was about to break.

Inky black darkness crept through the room, as if it were a tangible thing. Shadows lengthened and darkened as light disappeared. Every light extinguished caused the trepidation to grow. The darkness slid across the floor, over tables, drowning nearly the entire room in black. All the light that remained was the faint glow of a single light lacrima in the corner. It was all the light he needed.

Gray's hands shook as he picked up a sharp blade from the table. He all but stumbled over to an intricately drawn summoning circle. Steeling himself, he took a deep breath and pushed away his uneasiness as he lowered the knife's tip to his palm. He dug the knife into his palm with deep resolve. Ignoring the sharp pain lancing from the single point, he pushed harder and jerked the knife downward. Blood immediately sprang up at the deep cut, following the knife's path.

Tossing the bloodied knife away without so much a grimace, he turned his palm down to face the earth. Gray watched with cold indifference as fat droplets of blood spilled down the tips of his fingers and dripped onto the floor. The carefully drawn, white, overlapping lines of the circle quickly became red as his blood splattered over the floor. His hand was burning with sharp pain, but none of it fully registered as Gray stood, staring down numbly.

Shaking his hand, Gray didn't bother bandaging it. It didn't take precedence over the summoning, not in the slightest. He… this was his only chance. It was the only way. Gray pushed away the memories that surfaced to his mind. They would surely bring an onslaught of unwanted tears, and he could not afford weakness now. Not in front of a demon.

Swiping at his eyes, he fell to his knees a hair's breadth from the circle. Pain shot up from his knees, but he ignored that as well as he forced his expression into one of apathy. Holding out his hands, palms facing down, Gray dipped his head slightly, raven locks falling over his closed eyes. Calling on his magic reserve, he focused all of it at one single point; the circle. Heart pounding, mouth dry and body trembling ever so slightly, Gray clenched his teeth as the circle began to glow with ice blue light. This was it. Now or never.

Opening his mouth, he began the chant that would supposedly open a gate to the Underworld. Gray didn't give a shit about that; all he wanted was to summon a demon. He hesitated for a moment before forcing harsh sounds of demon tongue from his mouth. It sounded pretty good to Gray. It had taken months to learn. Finally, in his own language, he ended off the first part of the spell.

"Open, Gate of the Underworld!"

Gray's voice hitched as his impassive face became twisted with anger. A sudden surge of complete and utter uselessness flowed through him as he suddenly recalled the incidents that led to this, before it was quickly washed away by a wave of cold anger and thoughts of revenge. There was a reason he was in the middle of summoning demon, after all.

"I call a demon to aid my wrath,

A creature with me to walk fury's path,

A being to devour my past,

Come, Demon, I summon thee!"

Opening his eyes, he kept them trained on circle. His mouth quirked up in a grim yet wry grimace as blood kept flowing from his injured hand to the circle, seemingly evaporating as it hit the ground. Meal for the demon, he supposed. There was no trace of his lifeblood within the circle.

All at once, the ice blue light of the circle bled to deep red. Flames erupted, streaking high up. Gray snatched his hands back as he stared as the blood red flames flickered violently. From amidst them appeared a tall figure, eyes of the dark form glowing red. It grinned, its teeth glinting. Gray, still kneeling on the ground, shook as he took in thing before him. He had done it. He had really done it.

The demon snickered. It was a foolish boy who had called him from his throne? Silly human. He had no idea what he had gotten himself into. Deciding to humour him, the demon contained his fire to the circle's edges. Then he spoke, his voice a deep, smooth sound. Like a serpent on ice. It was enticing.

"Who dares call me?"

Gray stood on unsteady feet, shaking his head once to clear the fear clouding his thoughts. He picked himself up and looked at the being directly in the eyes, refusing to show fear. "I, Gray Fullbuster, called you."

"Well then, Gray, for what purpose did you so foolishly summon me?"

Glaring defiantly, he answered, "I want to extract revenge, to put through misery the one who destroyed my family through the demon Deliora." His expression shifted from defiant to vicious. "I want to kill him." In his deep blue eyes, there burned a fire of determination fuelled by pain and anger.

END considered his words. This little squirt has some gall, he mused, claiming to want to painfully killing off an offender. He sighed. Of course, it had to be for something like love to have him feel such animosity. So predictable. "So? What about it?"

With a hint of incredulousness in his gaze, Gray glared. "I want your help, demon. Assist me in completing what I wish,"Gray demanded.

Feeling a flicker of annoyance, END looked down at the boy with disdain. Who did he think he was? Who did he think END was? END was most certainly not just some run of the mill lower class demon. And the boy dared to order him around already? The nerve. Perhaps he ought to teach the boy to fear before they went any further. Leaning forward, he allowed his fire to seep outside the circle and surround the boy, the crimson flames trapping him in a cage of fire. Eyebrows furrowed in irritation and slight anger, END stepped out of the circle and growled at the boy, form still shrouded in fire.

"Who do you think you are, boy? I am END. Learn to fear those more powerful than you, child. Know your place. I do not take kindly to pretentious attitudes." His sharp teeth glinted in the light of his fire, his eyes smouldering red, and his body looming over Gray. "You pronunciation of the demon tongue, by the way, is comparable to shit."

Gray shuddered ever so slightly, thought it didn't go unnoticed by the demon. Fear became evident in his eyes. He was finally starting to realize just what kind of demon he had summoned. Attempting to appear composed, he tried to ignore the searing heat of demon fire licking across his skin and instead, said, "What do you want in return? And to hell with it, I don't give a shit about pronunciation."

END was slightly impressed. Not backing down? The human had some steel in him. Perhaps this will be worth leaving his throne for a little while.

"Hmm… I like you, little human. You have fire in you. Looking so brave in front of a demon such as I."

"I hate fire. And answer my question." Gray punctuated the end of his sentence with a cold, daring, pointed glare.

Stepping out of his fire, END moved closer still to Gray. His appearance, Gray found, was surprisingly human. He was taller than Gray. He sported shockingly pink hair, sticking up in every way, sharp fangs, and of course, startling red eyes. Black demon markings covered either side of his face and down his neck. Ebony black horns protruded from either side of his head, curling back. A black cape flowed from his shoulders down his back, and his fingers tapered into claws. Black scale like markings ran all the way down his arms and onto his exposed chest and torso as well. Black pants covered no doubt black marked legs.

Gray suppressed another shudder as he stared at the fearful being before him. Human looking or not, this was a powerful demon. Gray felt it in the demon's fire, his appearance, his stance, his presence. He even saw it in those eyes. END, ever observative, smirked and leaned in close to the human's face. He grinned wickedly, and his tongue forked out to run over his fangs.

"I want you, Gray Fullbuster."

Gray recoiled in disgust, anger and confusion evident in his expression. END chuckled. "Not in that way, dear boy. I want your life. Your being. I want your very soul."

Gray was stuck on one word. Soul. The demon END wanted his soul. That was a high price to pay for revenge… but it was something that Gray needed to do. To avenge his family, adopted or biological, he would pay whatever price the demon set and do whatever it took to accomplish his wish. If that's what it took, if selling his soul was what was required, then fine. The ends would justify the means, Gray was sure. He didn't need his soul. The demon could have it if it wanted.

"Fine."

END cocked a brow in curiosity. "You would break the taboo for something as trivial as love for dead people and hatred for a demon?"

Gray snapped. "My love for my family is not a trivial matter, demon. Of course you wouldn't be able to understand things such as all those you loved dying. They were completely innocent and had done nothing to incur what happened. Deliora destroyed my entire village; even all my friends and neighbours died." Gray gave END a dark look, full of loathing for the dead demon. Determination burned away the fear. Fury and hatred bloomed in his eyes as well. When he continued, there was a touch of poison in his tone. "I swear, I will destroy them. Whoever did it will pay for their crimes." He held the demon's red-eyed gaze and clenched his injured fist, ignoring the fresh rush of blood and sharp stab of pain. "I want power. Power more than anyone else, to take revenge on the ones who did this to me and my family."

"Very well. I will assist you in accomplishing those… ambitions, and in return, you will give me your soul." END leered at Gray, peering down into those dark blue eyes. He was impressed with what he saw.

Gray, to his credit, didn't flinch when he noticed the demon inspecting him. "I have a few conditions." When the fire demon didn't answer, he continued. "One, that you protect me until I have extracted my revenge. Two, that you serve me in whatever I need. Three, that you never lie to me. "

END frowned slightly, thinking, Such boldness, demanding that I do whatever he requests. However, it's not like any demon would see him in the human world, right? "Those terms are acceptable." Then he smirked. "However, there is one thing you seem to be unaware of. A contract seal. I shall place it… on your –"

Gray looked at the demon, apprehension trickling into his thoughts. However, if it was needed to seal the contract, then a seal he would bear. "My right eye." That way, every time he looked in the mirror, he would always be reminded of the contract he had made with the demon and the promise he held for his family. He would be reminded to never give up, no matter how long it took, because he had his entire village to avenge.

END offered Gray a genuine smile, albeit a little twisted. "Then your right eye it is." The fire demon reached out a clawed hand, grasped Gray's head, and all of a sudden, a searing pain engulfed all of his senses. His eyes open wide but unseeing, Gray's body arched as he screamed. He screamed and screamed as shocks of pain coursed from his eye throughout his entire body, fire racing through his veins. Everything hurt so badly, the line between hot and cold blurred. It was searing hot one moment, and freezing cold the next. It was pain unlike he had ever experienced before. It seemed to last forever, but then all at once, it was over.

END slowly withdrew his hand as Gray came back to his senses. Gray reached up a trembling hand to his right eye, head dipping, hair falling forward to hide his eyes. He couldn't see out of his right eye anymore. He couldn't feel what had changed except for the fact that that eye had lost sight, but he knew that if he looked in a mirror, the fire demon's seal would be there.

Picking his head up, he saw that a most likely matching seal had appeared on the demon's right hand. Looking higher, he saw that the demon was staring down at him impassively. Gray drew himself up and allowed his hand to fall to his side. He looked the demon straight in the eyes, the contract seal on his eye glowing dark blue. Then he spoke, and this time, his voice held no anger, nor fear. The detached tone held a certain amount of determination.

"Now you serve me in whatever I ned. Help me attain revenge. Bring me victory, demon."

END's smile aimed to placate. "Yes, master."

"Call me Gray."

"Of course, Gray."

"What do I call you? Other than END."

END contemplated for a moment. Should he give a part of his actual designation? Or randomly choose a name for the human world? "You may call me the Great Demon Lord Natsu."

Gray stared with a hint of incredulousness. "What?"

END held back a sigh of resignation. The boy obviously had no sense of humour. "Call me Natsu. My name in the human world will be Natsu Dragneel."

Gray nodded once before ordering the fire demon to appear as a human being. END obliged as well as extinguished the red flames trapping his new master. Gray stepped back and began to dress his injured hand.

Studying the boy, END took in his appearance and assessed his magic. He was tall, END assumed – he really didn't know what height standards for humans were, had a head full of raven hair, deep blue eyes, a lean build, long, slim fingers, and from what he could tell from that short exchange, a smart mouth as well. He was quite a character. Gray was obviously terrified of END, though he did a good job in hiding it. He had a certain darkness within him as well; not something one found in most people. Most certainly a result of his dark childhood. His cold rage, interestingly enough, burned like a blue fire; slowly but surely building up to become an inferno. It was quite a contradiction to his magic. Ice devil slayer. How in the world had such a young human like him gotten a hold on that power? Who in the deepest depths of Tartaros taught him that?

END sensed that the boy wasn't far from mastering the rare magic either. That… was certainly something worth looking into. It certainly explained the largeness of his magic reserve. This kid had built up a lot of power for himself; so big that he was able to call a demon such as himself. Now that was impressive, for a human. So was his strength and resolve.

However, even with the magic power and drive this child possessed, END figured it would take more than just a few years for him to be satisfied with the results of his hunt for revenge. Perhaps it would take the entire span of his short, human life. Nodding knowingly to himself, END allowed a feral smirk to grace his now human face. Gray's hunt for the Black Wizard would take a while, he surmised. That didn't matter though. The fire demon had time to kill, and he had no doubt that the human would prove to be quite entertaining throughout the years. From what he had already seen, the ice mage had a far more interesting character than any other human he had ever seen, save for his sole relative and his almost family member. Sitting on his throne was boring anyway, and dealing with his underlings was annoying. He didn't mind this little… excursion. Not in the slightest.

Etherious Natsu Dragneel smiled to himself. The boy was so amusing. He sought revenge on the creator of the demon Deliora? Ha, as if. END chuckled. Gray Fullbuster knew nothing of the hierarchy and organizational ways of the demon world. He had no idea exactly who the King of the Underworld was, or the identity of the one he sought. Nor did he know who the demon he had summoned was. END was a powerful demon, and as a result, he was difficult to control. END did what he wanted, not what a puny human told him.

He had bit off much more than he could chew this time, the little ice devil slayer. However, there was no backing out now. He had already sold his soul to the demon standing in front of him, after all. Now, Gray Fullbuster belonged to END, Prince of the Underworld. He smirked. What the boy didn't know wouldn't lose END his meal.

Gray glared at the smiling demon. "What are you smiling at?" When END did nothing but say "Prospects," and smile cryptically once more, Gray turned away in anger. "Whatever. Clean up the mess here and prepare dinner for me, demon."

END's eyes glowed an ominous red in the thick, heavy blackness of the room. "As you command, master."

A/N: Oh hey! You actually read the entire thing! Thanks for that. Leave a review if you have time and tell me how I did!