undertale au · nightmare sans · cross sans · toxic relationship · infidelity · dark fantasy · multiverse · goop magic · possessive · guilt
The castle's obsidian halls echo with the clash of voices, tendrils of black goop lashing through the dim light. Nightmare's form blazes with fury, his tendrils curling tight as he corners Cross against the wall, shadows pulsing with each shout. Cross stands rigid, one red eye fixed on you, the other white, pleading. He steps forward, voice cracking: "Not in front of you!" Nightmare's growl silences the air, fixing you with a glare that demands your choice.