The central plot of "The Misfit of Demon King Academy" revolves around a grand deception 2,000 years in the making. The core twist of Season 1 is the revelation of the identity and purpose of Avos Dilhevia. This supposed 'true' Demon King is a fabrication. The name was created by the human hero, Kanon, who Anos made a peace pact with. After Anos sacrificed himself, Kanon realized humanity's hatred for demons was too deep and would not fade. To protect Anos's future reincarnation and ensure peace, Kanon allowed himself to be killed by humans, then set up a plan to reincarnate over and over, eventually taking on the identity of Avos Dilhevia himself. His goal was to become a false Demon King, a common enemy for humanity to unite against, and then allow himself to be 'defeated' to finally bring peace, thus preserving Anos's legacy and the world he wanted. Anos's classmate, Lay Glanzudlii, is the current reincarnation of Kanon.
The true villain of Season 1 is not a demon, but a human named Jerga. He was a follower of Kanon whose hatred for demons was so immense that even after his death, his will persisted. He created the Hero Academy and its brainwashing curriculum to perpetuate the war, ultimately becoming a collective consciousness of human hatred that Anos and Lay must defeat together.
Another key reveal is the nature of Misha and Sasha Necron. They were originally a single being. Ivis Necron split them at birth using forbidden magic, with the intention of creating a more perfect vessel for the Demon King's reincarnation. Misha was the part designated to be erased, fated to fuse back into Sasha on their 15th birthday. Anos defies this fate by using his magic to travel to the moment of their origin and alter it, allowing both to live as distinct individuals.
Season 2's plot reveals the involvement of the gods, particularly a God of Heavenly Father, Nousgalia, who seeks to destroy the 'misfit' Anos and reinstate a divine order. The Avos Dilhevia of this arc is a different entity, a Great Spirit created from the wishes of the half-demons and spirits, embodied by Misa Ilioroagu, who seeks to create a world where she and her kind can belong. The finale of the first half reveals Anos's power is great enough to destroy the 'order' of a god, establishing a new cosmic hierarchy with him at the top.