World Trigger, Vol. 4

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. Should Border admit a Neighbor into its ranks? Jin and Arashiyama Squad think so, and they clash against headquarters’ top agents to preserve Yuma’s right to enlist.

After a brutal fight against his friends and peers, Jin makes an unimaginable sacrifice to put an end to the hostility and protect Yuma’s future at Border.