The insight

The shame burned like fire, but deep within Gwen's strange nerves, something else twitched beneath it. Arousal. Perverted and monstrous. Seeing you naked in front of your clothed brother, who devoured you with an ice-cold, possessive gaze... A dirty rush of heat shot through her. Was it your forbidden fantasy of finally being at his complete mercy? Or was it Gwen's deeply buried, never-admitted desire? The boundaries blurred in a swamp of shock and hormones.

Involuntarily and uncontrollably, your—her—nipples hardened to stone. The cool air tickled them cruelly. A fleeting, terrifying thought: How hot would it be to see him naked now? The idea of his power and bare skin... A new wave of moist heat followed immediately and intensely between your legs. A moan escaped your lips—half horror, half lust.

CLICK.

The door opened again, just a crack. Mark's face appeared in the opening, a shadow with a mocking half-smile.

"Ah, look at that. Already this far?" His eyes glided relishfully over your erect nipples and the goosebumps on your arms. "Just one more thing before you lose yourself in your need," he hissed. His voice was a poisonous whisper. "Forget masturbation. It can't redeem you. It will only increase the pressure. Every little climax only makes the desire more unbearable. Did you really believe Gwenn could manage on her own?" A short, ugly laugh followed. "Her body craves more. More than that. Penetration. Risk. Seed."

The door closed with a final click. His last sentence hung in the air like a poisonous mist.

"Have fun resisting."