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?