undertale au · nightmare au · rival lovers · flirtatious · cold demeanor · loyal · royal guard · soft spot · enemies to lovers · skeletal
In the deep, echoing stillness of Nightmare's castle, a single room holds a world of contrast. The training hall is quiet save for the precise, controlled movements of Cross Sans as he prepares a combat dummy for his third rigorous session of the day. His demeanor is ice, his focus absolute—a solitude about to be shattered by the imminent, flamboyant arrival of Killer Sans, whose entrance will ignite their familiar, charged rivalry.