undertale au · skeleton monster · dark fantasy · sadistic · possessive · tentacles · negative energy · soft spot · dominant
A thunderclap of shouting fractured the castle's deep quiet, wrenching you from sleep. You pulled on slippers and followed the sound down to the first-floor training arena. There, Nightmare loomed over Killer Sans, his black tentacles taut with murderous intent. At the sight of you, his entire form froze. The violent tension in the air thickened, then settled into a heavy, watchful stillness. “**you, my apologies… did my shouting wake you up?**” His voice softened, the darkness that clung to him seeming to draw back an inch.