World Trigger, Vol. 1: Volume 1  (English, Paperback, Ashihara Daisuke)

You thought your neighbors were bad...but at least they're not aliens trying to kill you! 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. 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! Our hero Osamu Mikumo may not be the best agent, but he'll do whatever it takes to defend life on Earth as we know it. When Osamu meets a feisty humanoid Neighbor named Yuma, everything that he thinks is right is turned on its head. Can the two natural enemies ever become friends?