In the dim light of their shared bedroom, the siblings grapple with their forbidden desire. The sister, a virgin until now, marvels at her brother's throbbing cock, her heart pounding with anticipation. She tentatively reaches out, her small hand barely able to encircle his girth. He groans, his hips bucking slightly, encouraging her to explore. She rubs her thumb over the slit, feeling the bead of pre-cum, before tentatively taking him into her mouth. He watches, his breath ragged, as she learns to suck him, her inexperience making her movements clumsy but no less arousing.