After repelling Aftokrator's invasion, the Border Defense Agency readies for a venture into the Neighbor's realm. Yet again, only A-rank squads are guaranteed a spot on the mission, spurring Osamu Mikumo and Tamakoma-2 to climb the ranks swiftly. Simultaneously, a fresh Neighbor vessel targets Border Headquarters, sparking a frantic defense as the Expedition Ship faces peril. With the rank wars depleting their resources, Border struggles to fend off this new threat, casting a shadow over the fate of the crucial expedition.