The system is a home-brewed, heavily modified mash-up of the various D&D versions I’ve played over the years. The setting could be similarly described.
The underground city of Twilight Vale is the only known refuge for those who survived the obliteration of the surface world. With the land above scarred, barren, and covered in magical radiation, the citizens of Twilight Vale must contend with the dangers found below if civilization is to survive.
Those with special training, powers, or abilities are given the duty of protecting the city and its people, from wandering creatures that burrow into the city as well as internal miscreants. Wielders of magic are required to donate a portion of their power to the city’s capacitors, which power the wards that block radiation seepage, the magical filters that clean the water supply, the city’s lights, and more.