The Misfit of Demon King Academy, Vol. 8 (light novel)

Thanks to the power of the people's wishes extending past kingdom borders, destruction was avoided, and peace has fallen upon the underground world. But there are many unsolved mysteries surrounding the death of the Goddess of Creation, the remaining Selected Eight, and the identity of the self-proclaimed father of the Demon King. Anos and his followers head back underground in search of clues and discover the existence of Erial--Stars of Creation that have Anos's missing memories sealed within them. But the land where the stars are hidden is controlled by the Sorcerer King, a powerful demon from the Mythical Age.