This used to be a famous and well-respect school, but the glory days are long gone. Nowadays, the place is more like a gathering ground for delinquents, and bad students.
The teachers are fed up, and they decide to rebuild from scratch and cleanse the place for good, with chaos. They introduce an “all-you-can-fuck” scheme. For a flat rate, you are able to fuck any girl in the school. As long as you pay the flat-rate fee.