For half a decade, a mysterious war has raged against an enigmatic foe, unbeknownst to the secluded inhabitants of Aoshima Island. Abruptly, every Friday at the fifth hour, scholars are plucked to battle at the forefront, shattering the island's peace. Among them, Saku and Miyako are deemed ineligible for deployment under veiled circumstances. In a twist of fate, Reina, a Tokyo escapee, becomes the initial envoy hurled into the heart of the conflict.