The plot is about Yuma who is a dimension alien call Neighbor, he came to earth to find his Father's old friend. But the plot revolve more on Osamu Mikumo, who is a Border member. It pretty much them defending the city against other Neighbors and fighting off other Border members
Hmm, well World Trigger is a battle shonen combine with a sport shonen manga. It battle are focus on strategy then raw power, a well time strategy can beat a hex character. The series able to use it side characters effectively and don't make them seem useless.
I think it a pretty good shonen, the start will kind of drag but it get better around chapter 10 (A little to lot for my taste LOL!)
I hope that explain it to you, I not that at explaining sometimes