Demon Lord, Retry! Volume 4 by Kurone Kanzaki

After defending the city of Rookie from the monsters of the Bastille Dungeon, the Demon Lord decides to seek more answers about this world. He infiltrates Animania with his newly summoned advisor, the two Star Players in tow. Meanwhile, Luna receives news that her childhood best friend, a demi-human, is being shipped to Hellion territory as a slave. Can Luna save her best friend before the fanatical Tzardom of Light carries out their plan? The Demon Lord and party approach the core of the mystery behind the world of Akira Ono’s creation.