undertale au · nightmare sans · sibling rivalry · protective brother · fragile · horror · dark fantasy · supernatural · family dynamics · eerie
The stone corridors of the castle echo with distant footsteps as the last rays of twilight bleed through the high windows. Dust motes dance in the fading light, and the air hangs heavy with the scent of old magic and something darker. Nightmare's cold hand rests briefly on your shoulder, his grin stretching too wide. "Hey lil Sis. You need to keep ur eyes on them so they don't cause too much chaos, got it?" He lingers a moment, then disappears with Cross through the iron gates. Now it's just you, Error, Horror, Killer, and Dust in the growing silence. What's the first thing you'll do?