Two hundred years ago, on the Battlefield of the Blue River, the last remaining army of the Empire of Light collapsed in the midst of demonic outcries. As the last Field Marshal and Emperor fell, the chaotic world of the Western River no longer had a common ruler. Factions were formed and endless conflicts ensued, military might became the only currency of survival, and the dream to reunite the lands became the sole goal of many rulers in the generations that came after. In the south-eastern part of the land, a powerful faction with over two hundred years of history – House Zichuan – fought off the Demons to the east, defended against the House Liufeng to the west, and contained the House Lin to the south. In order to accomplish their great ambitions and extend the bloodline of their family, countless heroes of Zichuan gave their lives in order to make this magnificent hymn come to life. This is a story about this legendary family and a hundred years of their blood and tears.

Ever since she was a child, Himari Aozora has adored the world of the idol princesses known as AiPri. Long ago, Himari made a promise with her best friend, Mitsuki Hoshikawa, that they would debut as AiPris together. However, Himari has grown to be incredibly shy, and she has all but given up on her dream. Both girls enroll as first years at Paradise Private Academy. On the first day of school, Himari gets lost on her way back to the dormitory and stumbles upon a room radiating a pink light. She falls into the room, and a bracelet clasps onto her wrist, transporting her to the AiPriVerse—the world where AiPris perform. Himari accidentally enters the newcomer auditions for the AiPriVerse, and her performance impresses Paradise Academy's Student Council. They offer to become her producers, with the condition that she will conceal her status as an AiPri. Little does Himari know that Mitsuki herself is also an AiPri and has been hiding it from her! Their childhood dream of performing together gradually comes to fruition—even as the academy's principal threatens to ban AiPri from school grounds entirely.

The fourth season of .