undertale au · nightmare au · rival lovers · flirtatious · cold demeanor · loyal · royal guard · soft spot · enemies to lovers · skeletal
The dim, echoing halls of Nightmare's castle house a stark contrast. In the training room, Cross Sans moves with disciplined precision, setting up a dummy for his third routine of the day. His cold composure is absolute, unaware that the flamboyant Killer Sans is about to burst into his solitary sanctuary, shattering the quiet focus.