A/N: He is going to have a book all his own, so I'm going to summarize his story as best I can. 

WARNING: His story involves sociopathy, violence, abuse, deception, manipulation, and obsession. 

In a universe different from ours, there was a small farming family; Father, Mother, elder brother Yooko, and younger brother Naran.  Yooko worked with Father year-round, hunting whenever the field didn't need to be tended. Naran worked more with Mother, helping with cooking and cleaning until the field needed additional hands, at which point he'd help his brother and Father.  Yooko strongly disliked his brother, but Naran didn't realise this, seeing Yooko's actions towards him as the actions of a loving brother.  

As they aged, Naran's adoration for Yooko grew, and Yooko grew resigned to it. He avoided Naran when possible by spending time with his girlfriend. Yooko grew up to a be a strong hunter with deep blue eyes, tan skin, and sun-bleached blond hair. Naran developed to be slim, yet well-muscled, with pale skin, ice blue eyes, and dark brown hair. 

Around Naran's eighteenth summer, Mother grew ill. She got sicker and sicker, and eventually died. Naran was distraught. He didn't think he could go on. He spent less time outside, and more time with books, trying to find a way to bring her back. He stopped going to town with Yooko and Father. He took over all the cooking and cleaning in their home. He ate less. He barely slept. He became malnourished and depressed. He did his best to hide it around Father and Yooko, however. He'd claim he had eaten earlier, or that he slept before he started cooking. 

For nearly two seasons of searching, he found nothing to help bring his mother back. Until one of his old friends came by for a chat. They were too chipper. He didn't feel comfortable with them anymore. Before they went back home, they gave him a book, saying "It might help you feel better." He looked it over, and it turned out to be a collection of stories about summoning demons. Pah! Stories for children. He threw the book into the fireplace and began to prepare dinner. After his father and brother arrived, they ate in front of the fire, and then went to their respective bedrooms. Except for Naran. He sat and watched the fire until it went out, at which point he lit some candles and started to sweep up the ashes. Inside the pile of ashes was the book. Undamaged from the fire or ash.  He was intrigued, and spent the whole night and ten candles looking through it. 

The next day, he slipped out of the house after his brother and father left, and began collecting the supplies need to summon the demon Nervos. He collected all the ingredients without trouble. Except for one. The fang of a leopard cat. This one took more preparation, but he was sure he could do it. He was caught off guard and attacked by the beast, but his father and brother showed up just in time to save him and kill the cat. His brother was mortally wounded in the fight. 

He frantically retrieved the fang and summoned the demon, but when it asked what he wanted, Instead of 'I want my brother to be alright' he heard himself say "I want ultimate power."

In trade for this, the demon took his father's mind, body, and soul, but Naran didn't notice. He managed to save his brother's life by shoving some of his newfound power inside of him, but his own body was weakening. He started to stumble away,but he collapsed, and his body fell apart from the roiling magic inside of him. His soul managed to latch onto his locket and remain, but his body was left as nothing more than an ashy mess.

When he came to, he felt invigorated. Powerful. The stress of the magic that had been tearing him apart from the inside out was gone. Or maybe, he had just stopped caring about it. He felt like a god. Like the most important creature in the universe. So he took a new name. Eonis. Naran was dead. 

It turned out he couldn't get rid of his old name. It was stuck with him forever. Written on his very soul. So now, whenever someone called him by it, he fell for them. They became the most important person in his life, second only to his brother and himself. He'd do nearly anything for them. The only ways to make him stop was to die, at which point he'd take your soul and put it in a jar, that he stored in his home in a pocket universe.

After a century or so, Eonis discovered his brother had raised a family. He was furious, so he searched for their home, and after he was sure Yooko wasn't inside, he started an electrical fire that began devouring the house instantly. He felt a soul inside the house began to scream, and his eyes widened,  before a smug grin split his cheeks. He burst into the house and made directly for the soul, pulling her from her body, and leaving the house ablaze.

The girl, named Tilly, stared at him, confused, but before she could say anything, Eonis explained that he was her great-uncle, and had felt her soul in horrible pain, and saved her as best as he could. She was surprised, but asked if he had seen her sister in there. Eonis faked a sad expression, and lied to her, claiming that she had also been in the house, but that Eonis hadn't been quick enough to save her. Tilly was heartbroken. Eonis offered to take her travelling with him, and gave her a new body.

She chose to accompany him, and traveled with him for two decades before Yooko and her sister confronted Eonis on taking Tilly from them. Eonis willingly gave Tilly to their care, but she had changed immensely in those 20-odd years. Eonis had twisted her spirit and mind, making her am entirely different person.

After another thousand years of small, boring trades and thousands of souls, a war broke out across his universe's Eurasia. The armies on both sides summoned him, asking for his aid, and he accepted both offers. So, he waited until the battle was at it's height, and forced a mountain to become a volcano, completely decimating the battlefield and covering the entirety of the connected land in molten lava. Two of the seven continents were now uninhabitable.

After Eurasia's destruction, an Australian man and his family, who all fervently worshiped Eonis as if he were a god, summoned him, asking for him to bring fiery judgment upon those who worshiped false gods. Eonis was flattered, but, as he was no god, simply an extremely powerful demon, summoned two dragons, who proceeded to destroy the man's house. The two dragons bred unhindered, and soon the entire population of Australia were dead or in hiding. Another continent down.

Because of Eonis's meddling, the earth's heat grew unbearable, and the ice at the poles began to melt, while the equator grew hotter and hotter.  Those who lived in countries without air conditioning began to get heat stroke, and either die or go mad. Africa was the worst off from this, with their crops dying and water evaporating, and soon even their countries unaffected from heatstroke were starving and their population died in droves.  Quickly, the cities were deserted and any survivors were dead in mind, if not body. Fourth continent gone.

After an additional century and millions more souls, Eonis was bored and tired of all the nothing that was happening. So, he took over the entirety of North America, threatening to destroy them if they didn't obey. He ruled for several centuries until there was the faintest rumor of a rebellion. When he was informed of this, he turned on every television. At which point, he used  a camera to stream video to every single one, and forced them to watch as he tore South America apart, before setting the remains ablaze, with the warning, "You're MINE. Don't forget it." Continent five decimated.

He continued to rule the continent for millennia before growing bored again. Eonis located his brother, and then he announced to the world he was leaving, and tore open a portal to another universe.  He shoved Yooko through the portal(who brought his descendants, at this point going by Hella and Loki), entered the portal himself, and then shut it forever, leaving the final humans on his world to their own devices. Soon after he left, the last of Antarctica melted away. Six continents perished by Eonis' fickle hands. 

He , Yooko, and Yooko's descendants arrived in the new world without warning, frightening some human-like creatures away. He was intruiged, and snuck after them, leaving Yooko alone to fend for himself. He ended up at a cave, and when he peeked in, they seemed to be smearing something on the walls. He shrugged and left.

He traveled the world for a while, and eventually discovered a fellow demon. They conversed for a while, and then Eonis, seeing that their body was better than the human's he was currently inhabiting, attacked them. After a small fight he cut off their head and took their body for his own.

 He snatched a couple animal souls as he traveled from place to place, and eventually ended up in Egypt. He snatched the form of a passing wildcat, and snuck towards the strange creation in the sand. A human passerby caught sight of him, and started shouting in a language he couldn't understand. He hissed at it, puffing up his fur, and when it approached, he pulled his form back, so he seemed to disappear in a small puff of sand. The human seemed started, and it gazed around in confusion. He pulled together a new form, this one of his newfound body, and glared down at the small human. "What do you want, Human?" 

The creature started jabbering in its language, so fast he couldn't understand it. He opened his mouth to snarl at it again, but the human pressed itself into the sand on its knees, with its head in the sand. Eonis looked at it thoughtfully. He knelt down and took its head in his hands, reaching into his mind and copying its  knowledge and understanding. The creature was completely still until he released it, then it buried its head in the sand once more.

He followed the human to its home,  and gave it some gold as a gift, before wandering around its country. He continued giving gifts as he traveled, sometimes full cat, but sometimes a random mish-mash of parts. He stuck around for a while, during which one human found his true name, and wrote it down in a scroll along with an image of him. She later died and joined his soul jar collection. 

He left egypt, and in his travels he came across a battlefield, on which a female soldier, named Elizabeth, lay dying. He revived her, and 20 years later took her to be his servant, twiting her body into that of a naga, and changing her name to Lizard. 200 years into her existence with him, he grew tired of her and her tendancy to tell him off, and threw her into a volcano. 

She remained their for another hundred years before he retrieved her to teach his new servant, Phase, who he had twisted into a gaseous spirit.

He still wanders the universes, answering summons and making deals.