Long A/N ahead!
The majority of non-Fairy Tail elements are from -Tales of- franchise, though extensive knowledge is not required aside from occasional references. As such, this story is not categorized as Crossover. Rate T for now and there will be a branching point somewhere in the future for potential spin offs not jumping from worlds to worlds.
The main character (MC) is a creation and incarnation of Magnadeus, Lord of Abyss in Tales of Destiny 2. Again you don't need to play that game to know about him, just that his title is such and he reigns over a collective version of Hell from a selection of shows like Fairy Tail. Voice actors for Magnadeus and the MC are Isshin Chiba (better known as Jin Kazama from Tekken and DIO in Jojo Heritage for the Future) and Jun Fukuyama (Lelouch Lamperouge from Code Geass and Joker from Persona 5).
Due to the differences in the nature of Magic between his realm and Fairy Tail, Magnadeus uses an alternative Magic called Elementia Accumulation in order to use any elemental Arte/Skill/Technique (use same word 'Waza' in Japanese) other than non-elemental ones like Demon Fang (Majinken) and Tiger Blade (Kogahazan).
Arte mastery: Basic (Tokugi) = Advanced (Higi) = Master/Arcane (Ougi) = Mystic Arte/Blast Caliber (Hissatsu Ougi). Altered Arte (Henka Tokugi), which can be learned after mastering a unique altered Arte like Demon Fang = Soaring Demon Fang (Majinken Shouga), can happen at any mastery except Mystic Arte. This is similar to power levels of Dragon Slayer Magic spells. Regular Mages can learn Artes but they will function on a different principle compared to those of MC.
Elementia Accumulation requires him to be near a Mage using their Elemental Magic to absorb the residue elemental mana. Different elemental Artes consume different amounts of corresponding stockpiled Elemental Mana and the MC cannot use them if his reserve is empty. Later on he achieves Over Limit state, which is equivalent to Second Origin, and can perform Artes without any costs for a short period of time. MC can also use his own life force to act as alternate Elemental Mana. Other than his own Magic and Arte spells, Magnadeus cannot learn Fairy Tail's native Magic types or at best can learn the most basic of them in an extensive amount of time. This is among the few counters against Dragon Slayer Magic as Elementia Accumulation absorbs their Magical Elements and uses the exact magical biologies as Elemental Mana while Dragon Slayers cannot eat their produced elements.
There will be romance and pairings but at this state, it's still early for me to settle on these aspects. Alright, long Author Note is over. Let's dive into Emissary from the Abyss.
Millennia ago, Dragons were the rulers of the world and other creatures like humans were nothing but cattles to them. The then-wizards decided to rebel against the draconic beings by conducting a ritual to summon a powerful entity that rivaled Dragons in power. They hoped to summon the Celestial Spirit King, the most powerful Celestial Spirit. But their ploy was discovered by Dragons and the ceremony was botched. However, the Dragons were a step too late. One had answered the wizards' pleas.
He was Magnadeus, the Lord of Abyss.
Heeding the wish to destroy Dragons from his dying summoners, the golden-clad being turned to his soon-to-be preys. They immediately sensed the imminent danger and most fled the place saved for some overconfident individuals.
"Fufu, you are fleeing. Such bravery…" The summoned entity clasped his hand and suspended the flying creatures inside an semi-transparent captive sphere. After that, two gigantic planets descended and ascended from above and below the sphere respectively.
"Will be rewarded with death. Last Vanisher."
The planets collided with the frozen dragons and released an immense burst of energy that vaporized them on the spot and destroyed a good chunk of the mountain as a result. Magnadeus then pursued the rest and killed them with a flick of his hand. Thus began the first yet unrecorded war between humanity and dragons.
Humans drove dragons to the brink of extinction until a traitorous human king collaborated with his nemesis to imprison and bind Magnadeus in order to use the Abyss Lord's powers for his own gain. He ordered the erasure of all records regarding this war and conducted numerous experiments on Magnadeus, who expressed nothing but uninterest towards the king's inability to extract his otherworldly power. In the end, he decided that both humans and dragons were the true enemies of this world and proceeded to annihilate the entire kingdom before sealing himself inside the depths of Earth out of sheer boredom for the lack of worthwhile entertainment inside a suspending ring called Infinite Time Prison.
Later on, in X300s, a young mage named Zeref, who was on his journey to discover a way to resurrect his beloved brother, stumbled upon the ancient ruins and accidentally unsealed the Time Prison, releasing Magnadeus from his slumber. Disappointed by the lack of a worthy opponent but impressed by Zeref's determination, the Lord of Abyss granted the young man the knowledge to create the magic formula that later became known as R-System.
"Interesting. Humans are now living in harmony with Dragons, then. A contraction…"
Intending to see how this played out, Magnadeus disguised himself as a wanderer named M. Some could say that he was on a journey to discover himself. Indeed, as much as his original aim was to see how this kingdom, Dragnuf, could maintain the 'peace' between humans and dragons, his true intention was to find a way to anchor his existence to this world permanently, not exhausting his (near unlimited) mana reserve every hour just to make his body solid.
"Princess of Dragons? How presumptuous."
M overheard someone shouting 'Make way for Her Highness, Princess of Dragons' from afar and snorted. Still, he was curious about whether this princess was a woman or a female dragon. Better yet, there was a swarm of dragons coming from the west with clear killing intent. A bloodthirsty smile slowly widened on M's lips.
"Finally, some action."
Irene, before she was known as the dragon witch Irene Belserion, was on her way to the neighboring kingdom of Christaf to see her soon-to-be husband, the prince of Christaf. When her maids began to panic, she lifted the window covers up to see a group of dragons of many kinds coming to her way. Before anyone could move, the sky darkened and divine lightning bolts struck down on the dragons, frying them on the spot.
"You are still alive…"
"Ah, look!"
She heard a calm voice somewhere around her and jumped out of the wagon despite the warnings from her guards to see who her savior was. There was a man in tattered coat floating in the air facing the surviving dragons, seemingly immune to their breath attacks.
"O violent gale born of fear… Now, why don't you run already?"
The earth beneath the dragons shook and cracked as the debrises were pulled upward by a pinkish tornado, swallowing the unfortunate ones and reducing them to dirt. The man laughed gleefully at the miserable state of the dragons while the cyclone continued to devour the rest of their swarm until none remained.
"Is this the power of this world's 'rightful' rulers? Pitiful. You don't deserve to see my true form, let alone a miniscule chance of winning against me."
It was that moment when he realized he had gathered an unwanted audience. The stranger turned to Irene as she had the most distinctive characteristic among the crowd.
"Princess of Dragons, attacked by dragons? How laughable. The harmony between humans and their oppressors is impossible." He lowered to Irene's eye level and touched her forehead with the tip of his finger, gaining the anger of her retinue. The princess could not object to this insolent behavior; or rather, she could not even move an inch. Something about this man caused her body and instinct to freeze as if being ordered to do so.
"Hmm, interesting. Very interesting." He chuckled. "Rejoice! You, princess Irene of Dragnof , have piqued my curiosity. Try your best and prove your strength to me, and you may earn the right to form the pact with Magnadeus, the Lord of Abyss."
And thus a butterfly had flapped its wings.