In a cramped, dimly lit room, two siblings learn the art of threesome training. The older sibling, a confident teacher, guides their younger sibling through the intricacies of anal sex. Starting with gentle caresses and kisses, they progress to fingering and rimming, preparing the younger sibling's virgin asshole. The older sibling watches, stroking their cock, as the younger one takes their first dick in the ass. The younger sibling gasps, eyes wide, as their older sibling slowly pushes in, filling them completely. The teacher's guidance is firm yet caring, ensuring their student's pleasure and comfort. As they find a rhythm, the older sibling reaches around to stroke their student's cock, bringing them both closer to orgasm.