A tiny house in Country Bray, Wicklow, Ireland.
A boy tuned 8 years old that day. His parents would likely bring him sweets or new shoes to celebrate, if he's not punished for being awake and out of bed. He tiptoed into the living room to perhaps fall asleep on the couch.
There would be no sleep from here in. Moonlight flooded half the room, the rest awash in shadows. The boy knew he would not be alone for long. He wouldn't hear the footsteps of his "Guest" and waking his parents proved futile. They could not see him.
Young Fergal could feel him. A dark presence that crept through the shadows and would toy with him some nights, usually right at midnight or just before dawn. Always when his parents weren't present, though, so they would not catch him or worry their son was haunted.
Every night before bed he'd ask for a small teddy or some other stuffed toy to try and ward this guest away. Though it didn't work, at least he didn't face it alone.
A faint creak in the floorboards his only warning. He wasn't strong enough yet to push the couch to hide behind. He slipped over the armrest away from the door and peered across the room to the silent TV, where he could hope to glimpse this visitor first.
"shhhhh....." a ghostly whisper tickled his ears. He shivered, tearing up.
It found him first. Again.
He looked at the TV screen; though dark, it reflected the room but no sign of his visitor. He peeked around the couch, only for a very black shadow fall over him.
The figure looked human in shadow; a man wearing a tasseled hat. The moonlight intensified to reveal that this was no mortal man. Its ice-blue eyes playfully shimmered in the moonlight, the tassels of his crown waving in an ill wind. Its lithe body graceful in its gestures, black clawed hands partially curled in uncertainty. Its human-like face had a slightly sinister smile, but the true scare came from the gaping maw that took up much of its torso. Serrated teeth, white and sharp, threatened the poor child as the maw's oversized tongue lolled out, a wet red snake tasting the air. The being kept just out of his own arm's reach as the boy's tears intensified. It didn't understand why Fergal did this every time he visited.
"This is a happy occasion," the creature said in Fergal's mind. "This is our Day of Creation...." he searched the boy's thoughts. "Birthday. When you were born, I was born with you."
Fergal looked up to the creature, still terrified and unblinking. It raised its lean arms, muscles flowing with the motion. "So you could say it. So say, 'Happy Birthday, Balor'."
Fergal shook his head no, worried that saying the creature's name would bring a curse. Balor lowered himself to his knees, closing in on the terrifed boy. "Today is our birthday. Humans celebrate that day. Why are you so scared? We have this together."
"If we're born the same day, how did you get so much bigger than me?" Fergal blurted out.
"Demons grow differently," Balor replied without missing a beat. "And one day we will be the same size." He crawled closer, the giant tongue seeking out the boy.
"You can't eat me on our birthday!" Fergal exclaimed, hoping to delay what he felt was the inevitable.
"Eat you?" Balor paused. "No. You are not my food."
"You can't eat mum and dad either!"
Balor's warm expression drooped with worry. "I will not eat them either. If I give you a present, will your eyes stop watering?"
The boy hastily wiped his eyes with the sleeve of his shirt. "What will you give me?"
"An oath, since demons break promises. I swear on my own blackened heart that no great harm will befall you. Always look forward and be brave, like the legendary Finn Macul; not over your shoulder in fear."
Fergal thought about that. "Do I have to get you a present?"
"Your friendship. I have sworn to not harm you. Friends don't harm each other, is that how it works?"
Fergal nodded. "Today is our birthday," the boy said simply.
"Today is our birthday," Balor repeated with more confidence.