On his first day back from summer break, ordinary high schooler Aoba Watase is attacked by a giant robot out of nowhere, and rescued by classmate Hina Yumihara piloting one of her own, who tells him only that "Dio is waiting" before sending him decades into the future. Aoba wakes up caught in the war between the Free Pact Alliance and the Zogilia Republic, and finds himself paired with a young pilot named Dio Weinberg. This manga adapts the story's opening arc.