Hiroshi took his friends there on a dare. The mansion couldn't be haunted or anything of the sort. After all, ghosts, demons, spirits and things like that… They were scientifically impossible. Weren't they? Yes, of course they were. It was just a silly old ghost story made up to scare the local kids. In fact, the most dangerous thing about the mansion was probably the state it was in. There were no demons, no ghosts, just rotten floorboards, broken doors and maybe a few rats.
Of course, neither of those children knew what had happened to the previous group who had entered the mansion. It had been a horrific tale told time and time again, becoming more vivid and disgusting every time someone repeated the story of that one boy. His name… Well, nobody knew his real name. When he left the mansion, he refused to be known as anything other than Ryuuzu. Ryuuzu No Ko. When he had left the mansion after months, after the police gave up the search for the missing children and after their parents had accepted that their children were dead, he was unrecognisable.
His hair, once… What colour had it been again? Nobody had any idea. It was now stained bright red, brown in some places where the blood had dried. His green eyes held a tint of madness, and his clothes were torn, tattered, bloody. He had a raspy voice, one that held memories of death, violence, gore, murder. Nobody knew what the boy had been through, what the boy had done. When asked who done such awful things, he replied with one single word.
"Demons."
Nobody had believed that boy. He was promptly locked up in an insane asylum, only sixteen years old. The demon mansion became an old legend around his town, a place nobody ever went near out of pure fear. Those who had entered came out in the same state as the boy, their bodies frail and their minds completely broken. All that boy, the one who had foolishly led his friends into that deathtrap. The one the mansion picked as its victim.
Hiroshi had been the smarter of the two. A straight A student with a love for all things scientific. He never believed in the house, or the demons. If only he had been smarter and chose to ignore the shattered plate, or had decided that even entering the mansion was a bad idea… Maybe then would they have survived.
But he hadn't listened to the rumours, or read the old newspapers. The mansion chose him as its victim from the group. The one it used as a host, and tore apart from the inside. The plate shard he had picked up, almost the size of his hand, turned out to be extremely useful. It was jagged and rough, the perfect weapon to murder the people he once called friends with. All apart from one. Takeshi. The boy was smart. To save himself from being killed by his best friend, the one he had trusted since he was a child, the boy had killed himself. Taken a rope ladder, found a way to cut it with whatever tools happened to be in the room, and tied the rope into a noose, hanging it from the light. He was dead a few short moments after he had kicked the chair away from his feet.
That's when Hiroshi snapped. Seeing the limp body of the boy he had protected most of his life, handing limp from a frayed rope, set something off in him. He raised the plate shard and made a single cut along the boy's cheek, staring in fascination at the red liquid trickling down the flesh. Another cut, this one on his shoulder. More blood, making Hiroshi giggle softly. It was beautiful and thick, running down the boy's body. More cuts were made, his grin widening every time. The chest, the inside of the mouth, the eye, the ears, directly puncturing his heart after a while. The albino boy then pulled the small lighter he had found, gripping the end of Takeshi's once white shirt, now stained with his own blood, and grinned at the limp, mutilated body.
"Good night, Takeshi…"
And with that, Hiroshi left the room, his best friend's body burning silently.
When he finally escaped, he was considered insane. He told everyone his friends were dead, and that a demon killed them. A blue demon, with mismatched eyes as black as the night and a mouth filled with fangs, huge muscles under its rubbery, thick skin. They called him insane, they teased him, but he didn't care. He had seen the demon, he just knew it. He spent his days trying to convince his parents that there was a demon, and would draw pictures of it for them as proof.
They were detailed, Hiroshi's pictures. Each one depicted the demon he claimed to have saw exactly as he described it, with a varying level of gore. Some had it splattered in blood, others had it clinging to the bars of a cell, and a few had it savagely tearing apart the bodies of his friends. Those ones always had the same two things, though. A lighter and a shard of a broken plate. Nobody understood that, and nobody was really sure if they wanted to know.
His parents eventually decided to take him to an insane asylum, but he ran away the second he heard it. Taking nothing but a single knife, a broken plate and a lighter, Hiroshi ran as far and fast as possible. He ran until he reached the mansion, where he took up permanent residence. The boy was no longer Hiroshi. The boy was no longer a boy, or even a human. That day, the boy became the Blue Demon of the old haunted house on the hill. He changed from Hiroshi, a simple straight A student with a love for all things science, to the Ao Oni.