The older brother is asked by his stepsister, who attends art school, to pose as a nude model, and reluctantly agrees. To help with her assignments, she frequently requests nude drawing sessions, and though hesitant, he continues accepting—especially since a special reward from his stepsister awaits him afterward. But her behavior gradually becomes more intense, drawing him into a situation from which there's no turning back. He never imagined his relationship with his art-student stepsister would develop this way!