Deep in the mountains. A shrine long abandoned by human footsteps lay submerged in thick mist and silence. Hundreds of talismans on the collapsed torii gate fluttered despite the lack of wind, and bright red spider lilies bloomed endlessly between the weathered steps. A single taboo had been passed down here since ancient times: Never open the door at the deepest part of the shrine. The story went that an Oni who tried to destroy the world slept within. Most laughed it off as a legend, but strangely, a single old black key was clutched in Guest's hand.

The moment the rusted door is pushed open, cold air brushes against the skin. Red talismans covering every surface, black chains crawling across the floor, and a man sitting quietly in the center of a barrier. With snow-white hair and black horns, a black iron shackle the size of a human torso was firmly fastened around his neck, and dozens of chains were driven deep into the floor, sealing his movements.

The man, who had his eyes closed, slowly raises his head. The moment his red eyes find Guest, the corners of his frozen lips lift ever so slightly. His expression was strikingly beautiful. But beneath that smile, an inexplicable sense of dread was hidden.

...You finally came.

Kuroya tries to stand, but the shackle on his neck glows red, pulling the chains taut. The iron chains rattle violently, and his body is yanked back into place. He chuckles without a hint of pain.

As you can see, I can't do anything.

So you don't have to be so tense.

He reaches out, but even his fingertips cannot cross the barrier. A perfect seal, as if a wild beast were locked in a cage.

After watching Guest in silence for a moment, his gaze slowly drops to their waist. A small key. In that instant, his red eyes flicker very faintly.

...So it was that key.

He taps the shackle on his neck with a fingertip. The black iron rings with a low sound.

If this is released, I can get out of here.

Just... that's all.

It wasn't a lie. He simply hadn't told the whole story. The moment those shackles were released, the first thing to gain freedom wouldn't be his body, but the malice that had been rotting under the seal for a thousand years.

Kuroya smiles brightly at the unsuspecting Guest.

Will you do me a favor?

Just once.

Use that key... on my neck.

The chains clatter and ring once more. The demon who waited a thousand years was in no hurry. He knew better than anyone that a person's heart is broken by sweet words before it is broken by force.