The basic premise of my idea is "Chastity Show & Tell". In this universe, I live in a female-dominated family, you'd play my step-sister. Our matriarch keeps me in chastity, you and she are my keyholders, I'm only let out once a month (if I'm good) for supervised masturbation and you've brought me into your class for "show & tell".

1st: Me undressing, being to show the device to the class while you describe it's purpose. 2nd: Demonstrating the cage by teasing and frustrating me 3rd: Making me demonstrate my monthly supervised masturbation in front of the class.