Yukiteru was born in Hakodate to a pair of merchants. Being a port town, Hakodate was the perfect place to conduct their business: importing and exporting goods between Hokkaido and the mainland, Honshu. Since it was expected that their only child would inherit the family business, it was not long before they were preparing Yukiteru for his future duties. From a young age, he would help his parents keep stock and watch as they loaded and unloaded their ships. By twelve he was filling out ledgers and carrying smaller crates with minimal supervision from his parents.

Meanwhile, across the channel separating Oshima subprefecture from Aomori prefecture, a newly made demon by the name of Yokusai (慾斎) was struggling in Aomori city. Yokusai was progressively pushed northwards due to territorial demons competing for the limited populations which inhabited the northern parts of Honshu. Still too weak to face off with any of his kin, he eventually ended up in Ōma, the sister city of Hakodate. From Akaishi Beach he'd watch ships come and go, fantasizing about hunting grounds that were exclusively his, free from other demons or demon slayers. As men at the dock loaded ships with fishing supplies, inspiration hit him. The ships contained crates that would be kept below the deck, where the sunlight wouldn't reach. In the dead of night, Yokusai climbed aboard a docked ship and hid. The next day, it set sail for Hakodate.

When the ship arrived at Hakodate's port, it was devoid of any crew. This event, having already sparked gossip, was followed by months of disappearances as more and more townsfolk declared missing friends and family. This sparked the telling of ghost stories about a many-limbed apparition haunting Mount Hakodate's trails. Rumors warned about travelling at night, especially near the mountain. Even with townsfolk avoiding the mountain however, people continued to disappear one after the other.

But business proceeded as usual in the Fubuki household. Shipments had to be prepared the night before and made on time. Falling behind on even one shipment would slow them down for weeks at least. Therefore it was no surprise when Yukiteru's parents asked for his help late one evening. He follows them to the docks, carefully loading the ship. Having also caught wind of the various rumors, he keeps an eye out for anything suspicious, such as sudden movements or strange silhouettes. His father teases the boy for his skittishness before handing over the last box. Yukiteru descends down the ship's hatch one more time with a grunt of effort. This one was much heavier than the others, after all.

As he climbs back up, his foot loses traction and he nearly slips back down. Only when he's regained his balance does he notice the blood dripping down from the mouth of the hatch. Forgetting how to speak for a solid five seconds, he calls for his father and only silence answers back. He ascends with haste now, climbing out and onto the deck. The sight of his father motionless, his mother's body slumped over his, has him frozen in place. The blood was coming from them, and continued to pool underneath his feet. Though he tries, he cannot command himself to move. Neither towards them, nor far away from this place.

"Ooh, you're a quiet one," comes a voice from behind. It sounds like it's right next to his ear and also everywhere at once. The confusion keeps him paralyzed but his body trembles. "That's good, I hate the screamers."

There is a sharp pain at the back of his head, and Yukiteru blacks out.

When he comes to, he hears it before he sees it. A wet sound, slurping and chewing. When he looks, he wishes he hadn't. No more than a few metres away, a large man was hunched over his mother's body, feasting on the clinging pieces of flesh that were left on her forearm. Another body, most likely father's he belatedly realizes, lay further back, yet untouched. Bile burns at his throat and he swallows hard, overcome with disgust as the stench hits him, kicking his brain into full gear. How the sight and smell of those corpses could rouse any sort of appetite for any creature confounds him.

He takes a look at his surroundings. His own body was laid to rest upright, propped up against something cold and hard. Rock, perhaps? Grey stone surrounded them in all directions with a few furs and clothes littered together haphazardly, as though it were a nest. There is a draft blowing in from somewhere he cannot see, which he assumes is the entrance (and more importantly, the exit). This kind of layered stone could only be found on Mount Hakodate. Yukiteru steels his stomach and forces himself to peek at the man before him.

Deep crimson tendrils emerged from the small of the monster's back in a manner that vaguely reminded Yukiteru of spider legs. They had far more flexibility however, constantly in motion. One of these strange tentacle limbs was wrapped around his mother's ankle, adjusting her position so that the thing—Ghost? Apparition?—could get at the posterior's meat. The sight has him choke on his own vomit, finally alerting the demon to his very conscious meal.

The tendrils release his mother and the demon stands, swiping the back of his hand against his mouth. "My, where are my table manners! I hadn't even noticed you awoke."

He crouches down in front of Yukiteru, inspecting him. A tentacle, still dripping his mother's blood, slides under his chin. He had expected it to be slimy like a squid but it feels sharp and solid, so his discomfort is only increased as it forces his face from side to side. The demon hums appreciatively.

"You'll make a fine dessert. Just stay here, watch, and wait your turn, okay?" He rises once more before giving a thoughtful pause. "Oh yes, how rude of me. I'm Yokusai. What's your name, little one?"

Yukiteru does not answer. The demon, Yokusai, lacks the patience for it. The tentacle under Yukiteru's chin jerks back and then stabs into his hand, causing him to scream. Yokusai is laughing, delighted that the boy is no longer tight-lipped. "Your name?"

Heaving due to the pain, Yukiteru can barely muster an answer, but the pain he was in and the promise of more has him rushing to respond between breaths. "Yu... ki...teru."

Satisfied with the answer, Yokusai nods and then returns to the other two corpses. Yukiteru cannot do anything else but listen to the sounds of the demon's feasting and smell the coppery tang of old blood. The alternative was to fixate on a space that did not have his parents in his peripheral and numb his senses. To think and perceive nothing at all. There was no point in trying to escape. He could only hope that he'd at least be granted the mercy of not being eaten alive. Nerves no longer petrified by shock, he sobs silently, tears finally overflowing.

It feels like hours. It could have been days; Yukiteru isn't sure. Yokusai is suddenly in his space once again, snapping his fingers to pull the boy out of his daze. His grin broadens as Yukiteru finally focuses on him rather than staring past him. He starts talking about playing a game, and Yukiteru is trying his best to try and understand what he is saying, but the thought 'it doesn't matter' keeps echoing and drowning out the demon. There is no context for why he is suddenly being pulled to his own feet, nor for dragging him to the mouth of the cave and throwing him to his knees. He lands amidst some smaller shrubs and snow, smaller rocks hidden under the blanket of white scraping his knees. Bewildered, he tosses a glance over his shoulder, back at the demon.

This time, he can hear every word loud and clear. "I'll give you a headstart, okay? Run as hard as you can, Yuki."

Yukiteru scrambles to his feet and doesn't look back. His feet hit the ground and he runs, runs faster than he's ever known how. Though everything whizzing past him is blurred, he's never felt so focused or aware in his life. Every snap of a twig, every owl's hoot, everything could be seen and heard. And it all spurred him to keep running, to never stop running. He shuts his eyes and lets his instincts take over.

He's made a good distance down the mountain before he hears Yokusai in pursuit. The demon's tendrils collide with so many surfaces along the way—the trunks of trees, the crunching of snow, and even other animals—that it was easy to single out the abnormality in the mountain's fauna. A careless predator. Yukiteru does not slow down for even a second, only changing direction occasionally. There were more and more large trees in this area, indicating that he had almost made it to the base of the mountain. Light was beginning to brighten the sky's edges, and finally Yukiteru felt hope.

But he is knocked to the ground, face planting into the dirt and snow. Yukiteru gasps and pushes off his arms in an attempt to get up before a weight slams down against his back. Yokusai sighs, knee pinning the boy in place. "Wow, you almost made it! I'm so proud of you, none of my prey has ever made it this far before!"

But the demon sounds strained, out of breath himself. He truly struggled in keeping up with him, and now the sun was threatening to show up. His usually smug smile is pulled taut, forced. "I won't have time to take you back to my den, so I suppose a picnic would suffice."

Tentacles seize Yukiteru's wrists and Yokusai eases off the boy, flipping him onto his back. Yokusai looms over the frightened boy, licking a stripe over his cheek, salted with tears that have long since stopped coming. He wants me to watch, he thinks deliriously, squeezing his eyes shut. If this was the last act of defiance he could muster, that would be enough. When his clothing gets soaked in blood, he assumes that it's his own, and thanks whatever god exists that it was being done painlessly.

Then the weight disappears from him entirely, so reluctantly, he peeks through one eye. Yokusai stares back, but his body is no longer attached to his head. Yukiteru shrieks (higher pitched than he'd ever care to admit) and bats the head off of his torso. It falls apart before it even hits the ground, scorched ashes disappearing into thin air.

A masked figure now stands before him wearing the face of Tengu. Not any less creepy than the demon, but at least it didn't have strange protrusions snaking out of its body. It sheathes a blade and bears down on him, then holds out a hand. After this ordeal, Yukiteru is not sure if he wants to take it, even if it's the hand of his savior. He pulls his knees up to his chest and hugs them.

"Come with me, let's get you cleaned up." The voice is oddly gentle and soothing. Against his better judgement, he takes the stranger's hand. It's not like he had anywhere else he could turn to. His parents were long gone, devoured.

He soon learned the man's name was Sakonji Urokodaki, and he was a Demon Slayer.