In the dimly lit room, the young sister kneels before her brother, eyes locked on the thick, veined cock he's displaying. "I must verify your purity," he commands, voice thick with lust. She hesitates, then tentatively reaches out, wrapping her small hand around his shaft. He groans, guiding her head towards his crotch. She parts her lips, taking him in, her tongue swirling around the tip. His hips buck, forcing more of his length into her mouth. She gags, tears streaming down her face, but she's determined to prove her innocence, even if it means breaking her sacred vow.