You thought your neighbors were bad...but at least they're not aliens trying to kill you! 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. The away mission test heads into Day 3! Osamu and the rest of Suwa’s Squad 7 are struggling to handle the additional units in the battle-sim exercises, yet they’re managing to move up in the overall ranks. But what will they do when their ace, Katori, slips into a sudden, debilitating funk?!