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.

Yuma's Neighbor identity revealed, the Tamakoma branch safeguards Yuma, Osamu and Chika by recruiting them to their group of powerhouses and eccentrics. But Border headquarters wants Yuma's Black Trigger badly enough to send agents from its top three squads to steal it!