Let me just give you some advise, watch it 'til episode 12 because episode 13 and beyond will blow you away with a lot of action pack, especially the Invasion part where every episodes gaves a lot of tense, and unpredictable happenings.
Story takes place when Usamo met Kuga, a Black Trigger user who is also a Neighbor. Kuga came to earth to search for his Father's friend. Usamo help Kuga to find with him, but it turned out Kuga is also helping Usamu for being an Agent and put him in a lot of trouble for being a friend with a Black Trigger user. But their friendship became stronger as the story goes on.