Earth is under constant threat from Neighbors, invincible monsters from another dimension that destroy our way of life. At least we have the elite warriors of Border, who co-opt alien technology to fight back! Meet agent Osamu Mikumo, not the best, but along with his Neighbor friend Yuma, he'll do whatever it takes to defend life on Earth as we know it.

It's the final day of the battle simulation exercises, and the formerly superior Ninomiya's Squad 8 is in decline now that others are exploiting the weaknesses of Chika's units. While Chika grows more and more frustrated, Ninomiya himself is keeping tight-lipped about the whole thing... That night, it all comes to a head when an irritated Ema confronts Ninomiya!