[Furube] Kyoudai de Nichijou-teki ni Sex Shiteru (Part 4)

An anxious sister in a sailor uniform kneels on a bed, sweat glistening as a composed woman in a business suit watches from the doorway, hand over her mouth in surprise. The brother, caught in the act, begs for release while voicing conflicted feelings about his sister's academic focus and his own desire. The tension spikes when the mother bursts in, shouting that she's home, forcing the pair into a frantic scramble to hide their intimacy.