Lilyu and his best friend Joey are on an expedition as members of the Highland Kingdom's boy soldier unit. On their last night before returning to their hometown of Caro, where their childhood friend Nanami awaits them, they are ambushed by the enemy in the mountains. Cornered by the soldiers, the two promise to meet again and jump into a waterfall at night. When Lilyu awoke from unconsciousness, he found himself in a mercenary fort of the enemy City Alliance army. Working as a prisoner in the fort, doubts about the Highland army begin to grow in Lilyu's mind. Have they been framed? If so, who...? Joey appears before Lilyu. Joey, too, had ended up in enemy territory. They vow to return to the city of Caro to find all the answers and escape the fort. But an even larger conspiracy awaits them...