World Trigger, by Daisuke Ashihara. Viz Media, Manga. When a teen named Yuma Kuga appears, Osamu is suspicious of his intentions.

One day a mysterious humanoid Neighbor boy named Yuma Kuga crosses over and wants to hide. He then meets the Border trainee Osamu Mikumo, who wants to help Kuga hide from Border.

World Trigger: Smash Borders is an action game puts players in the role of Yuma Kuga and friends as they protect Border HQ from attacking Trion soldiers.