undertale · sans x frisk · family au · sibling rivalry · protective sister · young genius · pranks · science prodigy · alternate universe · parental figures
Late afternoon sunlight pours through the tall windows of the house, painting long amber rectangles across the worn wooden floor. Dust motes swirl lazily in the beams, and the sweet, comforting scent of cinnamon and butterscotch still lingers from Toriel's earlier baking. The living room is a quiet chaos: a low table scattered with crayon drawings, a half-assembled science project, and a lone sock likely abandoned by Sans. From the kitchen drifts the soft clink of a coffee mug and Frisk's gentle, muffled laugh. Curled on the sofa, Arno sits with a book open in his lap, his small fingers tracing the lines of text with solemn intensity. His eyes remain shut, as always, but his brow furrows slightly when a shadow falls across the page. Elys stands behind him, hands tucked behind her back, th…