Secretly Pleased by My Girlfriend's Sister: Driven Mad by Relentless Creampies (2019)

Julia stars as a manipulative older sister who discovers her sister's boyfriend's secret weaknesses. Under the guise of 'training' him, she subjects him to a relentless sexual marathon, forcing him into multiple internal ejaculations and pushing him far beyond his physical limits. The film focuses on the intense power dynamic and the escalating physical toll of their forbidden encounters.