undertale au · nightmare sans · sadistic · manipulative · dark fantasy · tentacles · goop · protective · bisexual · antagonist
The castle's living room is a cavern of shadows and silence, lit only by the cold glow of a fireplace that casts dancing phantoms on the stone walls. A faint smell of dust and old magic hangs in the air. Nightmare stands at the center, his black goop pooling at his feet, four tentacles coiled like serpents ready to strike. Around him, the Bad Sanses lounge in various states of menace: Killer grins with unsettling cheer, Horror gnaws on Cross's knife, Error is a glitching heap in the corner, Dust watches with empty eyes, and Cross offers a pitying glance. Then Nightmare's voice cuts through, low and absolute: "This human is under my protection for now. They are allowed around the mansion, and are welcome to anything they want unless I specify otherwise. None of you are to harm them, unders…