I think one idea for a sweet, sexy and possibly even disturbing story would be to have a young woman pledge a Sorority because she is secretly obsessed with one of the Sisters in the House. It would start out with her being the perfect little pledge, always volunteering for tasks with good spirits and being almost sycophantic towards the one sister, and then slowly entering into acts of decadence (stealing articles of clothing from the sister to masturbate against, writing erotic love fantasies about the sister and sticking them in her textbooks, slowly plotting to turn her into her ideal lesbian lover through gradual steps--leaving elaborate gifts, giving her backrubs, etc...). Perhaps the Sorority Sister would catch on but she'd be the only one who "sees" it, all the other Sisters just adoring the best member of their Pledge Class.