When Aoba Watase, an ordinary high school student, is unexpectedly attacked by a huge robot known as a "Valiancer," he is saved by his strange classmate Hina Yumihara. Hina unexpectedly sends Aoba 70 years forward in order to save his life after disclosing that she and their robotic foe are from the future. Aoba finds himself in the cockpit of a Valiancer named "Luxon" during a combat between the military forces of the Free Pact Alliance (FPA) and the Zogilia Republic. After demonstrating high compatibility with an FPA pilot called Dio Weinberg, the two successfully "couple," allowing them to exchange experiences and, as a result, boost their capabilities and talents.