Destroy thy Neighbour! A gate to another dimension has burst open, and invincible monsters called Neighbours 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.

It's a Neighbour invasion! Trion soldiers swarm Mikado City, wreaking havoc and capturing isolated Border agents. When the sinister humanoid Neighbours orchestrating the attack target Chika for her massive Trion, Osamu may be the only one who can save her! But can a B-Rank agent compete against the surprising power of this new alien foe?