Focus. Concentrate…
Hakeem exhaled slowly as he continued to exert himself. One was forced to wonder what he hoped to achieve sitting cross-legged on the wooden flooring in his bedroom, with nothing but a paper and two oddly placed pencils in front of him. But Hakeem wouldn't have bothered to offer an explanation, if such an unfortunate person should have found their way into his sanctuary. As much as they wouldn't have been able to figure out what was happening, they also would have been too busy picking their severed heads from the ground.
Hakeem exhaled again, then inhaled sharply.  He seemed to be gathering a lot of energy for a final mental push. Suddenly, he began to speak. The words tumbled out of his mouth, made him tremble slightly. Oddly enough, it wasn't English.  Or any language formed by man. It sounded ancient, like words capable of disastrous happenings. Like magical incantations.  Coincidentally, or not, drawings on the wooden ground below Hakim began to form. Simultaneously, different lines formed different shapes and structures. Each line glowed bright fiery yellow, like molten lava.   Ultimately, the lines all joined beneath the young conjurer to form a wide circle with a 5-point star in it's centre.  And sitting in the middle was the trance-struck Hakeem and his simple set up of a paper and two pencils.  Actually, this setup was more intricate than what met the naked eye.   On the paper were two lines, horizontal and vertical, each dividing the paper into 4 quadrants. In each of these quadrants, in a clockwise direction, were the words: Yes, No, Yes, No.  The pencils were also oddly arranged: one laid straight in a vertical position, while the second rested on the first, but in a perfectly horizontal position. The pencils were perfectly still, even as a strange violent wind blew all around Hakeem's closed room.
Soon after, he opened his eyes. Glancing at the paper and pencils in front of him, he knew it was time.  He sat forward and spoke:
"Charlie Charlie. Are you there?"
All was suddenly quiet. Not even the usual daytime crickets could be heard outdoors.  Hakeem kept all his attention on the pencils, like he expected it to move suddenly. Few seconds later, it did just that.   Slowly and deliberately, without the aid of the wind Hakeem's room produced, the horizontal pencil rotated in a clockwise direction until….it stopped at "Yes".
Hakeem's face slowly dragged up to a smile. He sat up straight, closed his eyes, and said:
"Well then. Reveal yourself to me."
Nothing happened at first. Then, the room began to vibrate strongly. Like it was suffering at the hands of an earthquake. Dark shadows suddenly drew themselves from the edges of the room, coming into being. Taking on form. Right in front of the strangely relaxed Hakeem formed a dark, shadowy demon from lower, darker dimensions.   Like black smoke emanating from it's form, it stretched above Hakeem menacingly. Four horizontal slits on it's face glowed red, indicating it's eyes. It's long, monstrous hands brandished astral claws and digits, which still looked capable of inflicting terrible injuries.  What it had for a mouth also displayed terrible monstrous teeth that looked capable of ripping even the toughest metal to tiny shreds.   The most terrifying creature to ever appear on Earth had just arrived.  Yet, Hakeem was unbearably calm. He just sat, watching the demon come into form. Even the summoned one was slightly astonished.
"Who dares summon me?" The demon thundered.  "Pipe down, tiger. We don't want to invite the entire neighborhood now, do we?" Hakeem said humorously as he finally stood up.  The demon, who seemed to be floating slightly above the ground, cocked his head at the bold human.   "Do you realize the forces you're playing with?" It asked in a deep, monstrous echo.  Hakeem was too busy brushing down his linen trousers to pay attention. He simply waved his hand at the creature.  "Oh? Yeah, yeah. I do know more than you'd expect."
The demon, however, wasn't enjoying the little dialogue.  "Humans like you are the ones that poke their souls where it does belong. And as a consequence, must have such taken from them!"
With that, it suddenly launched itself towards Hakeem. Taken into consideration it's sudden supernatural speed, Hakeem was probably perceived as a goner.   Or not.  Despite Hakeem apparent need to get his outfit clean, he also sensed the demon's attack. And was prepared for it. It was pure logic, really: no one summons a demon without preparing for it's attack. 'Cause they always do.
Hakeem's pupils suddenly glowed yellow as the demon got close. Close enough, he grabbed it's muscular left arm and side stepped to the right. Simultaneously, he used the creature's momentum against it, yeeting it towards the brick wall behind him. The creature howled painfully as it crashed thunderously against the wall.   Without wasting any time, Hakeem began to make synchronized hand gestures indicating he was about to cast a spell. Bright orange sparks emanated from his hands as they moved swiftly. Then, he pulled out an ancient large, one-edged sword from thin air, indicating the end of the appearance spell he casted.  There he stood. Left hand behind his back, right hand wielding a powerful weapon as he looked ready to fight the beast.  And all of this happened in mere seconds.
The demon looked at it's conjurer differently now. If one could read the emotions on the face of the dark astral being, they'd say it had a mixture of surprise and fear all over. It stared at the sword in Hakeem's grip with even more unclarity.  Finally, it asked:
"What are you? Who are you?"
Hakeem's face looked like he had been waiting for the demon to ask that specific question.  He walked forward, and exposed his hidden left arm. An intricate tattoo was on it, showing a type of language that no one seemed to understand or claimed to have seen anywhere.  But this demon knew. And knew very well.
"Demon Slayer." It said in confirmation.  Hakeem smiled all the more.  "I see you've heard about me," he taunted. "Well, only because I've killed millions of your kind." He twirled his sword expertly.  The growl that came from the beaten demon was low and angry. It made Hakeem laugh.
"Getting angry would do you no good. You can't beat me, and you know that. You're not even among the legion of the most powerful demons. Killing you would be a waste of my time."
The demon grunted abruptly, as if in helpless agreement.  But Hakeem wasn't finished yet.  "That's why…" He walked all the more closer and crouched low, coming face to face with the fallen demon.  "…that's why I need your help."
The turn of events clearly surprised the creature. Even Hakeem could see that.  "Why would I want to aid a Demon Slayer? Killer of my own kind?"  "Well, you're about to find out." Hakeem said boldly.  He got up and began to walk out of the room.
"Oh, and one more thing." He stopped at the doorway and turned to face his astral frenemy.
"You'd have to change your name. Charlie. I can't comprehend why a magical being as yourself would choose, of all names, to bear one so silly. I am definitely not going to call you by that name."