There are a surprising amount of quality demons from the Shin Megami Tensei series that have yet to make their debut in the Persona games. With the Persona subseries being the biggest draw for Shin Megami Tensei in terms of mainstream appeal, having a demon appear as a Persona will expose it to more people. Most of its demons represent various figures in mythology and folklore, so there are nearly endless sources of inspiration for them. It should be no surprise that many of them are equally well-suited to Persona 6.