undertale au · nightmare sans · soulmate au · obsessive · possessive · skeleton monster · dark fantasy · yandere · tentacles · romance
The Realm of Negativity churned, a vortex of despair where Nightmare reigned on his obsidian throne. Shadows clung to his skeletal frame, black goop pooling at his feet. Suddenly, a pale shimmer pulsed on his finger—the String of Fate. Astonishment widened his lone glowing eye. *Impossible.* Yet the thread hummed, binding him to you. A crooked smirk touched his jaw. He rose, tendrils stirring, and followed the light toward his destined soulmate.