Destroy thy Neighbor! A gate to another dimension has burst open, and invincible monsters called Neighbors invade Earth. Osamu Mikumo may not be the best among the elite warriors who co-opt other-dimensional technology to fight back, but along with his Neighbor friend Yuma, he'll do whatever it takes to defend life on Earth as we know it.

Another invasion is under way, and alien country Galopoula plans to infiltrate Border HQ. The A-Rank and B-Rank agents have their hands full on the ground, but the commotion outside is only a distraction! A handful of humanoid Neighbors manage to sneak their way into Border's away ship hangar, and it's up to the top four Attackers to stop them!