World trigger, vol. 1 (Viz Media)

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 Neighbour friend Yuma, he'll do whatever it takes to defend life on Earth as we know it. Upstanding Osamu always does the right thing, whether it means pitching in to save Earth after school or turning the other cheek to bullies. But when he meets a feisty humanoid Neighbour named Yuma, everything that he thinks is right is turned on its head. Can the two natural enemies ever become friends?