A story where the MC is a young teen girl that is free-used at her new high school. No discussion about it, used by both males and females, students and faculty, both between classes and during classes. She is initially confused, upset, etc about this happening to her and tries to complain, but it is as if no one hears her or understands the problem.. not the administration, not her parents, not police, nobody.
Key thing: the free-use is limited to school hours and/or school activities (ie on a school trip, the entire time would be free-use until returned back to the school).
She learns to accept it and love it. She also learns that there is one "free-use slut" in each grade level. Additional possibility: She learns that once "tagged" as one of the school's free-use sluts, it is a lifetime commitment - i.e. the free-use will continue to wherever she goes to college, her workplace, social clubs, etc ... anyplace that is not home or personal free-time... even after she is married - and no one will ever condemn her for it. She could learn that from an older woman who was selected a couple of decades prior and is still being free-used to this day... it could even be her mother and she realizes that she had seen her mother being free-used many times and never ever realized it wasn't perfectly normal.