Osamu reaches out to Yuma and Replica. He and Chika learn some critical information about Neighbors from Yuma, but they're soon discovered by two A-Rank agents, Shuji and Yosuke; they're searching for a Neighbor in human form...

Border sees the Neighbor Yuma as an enemy… but Osamu is unable to view him as someone with hostile intentions, and trust begins to bloom between the two boys. Osamu finds himself caught between his own thoughts and the rules of the organization he belongs to, Border.

Approximately four years ago, a gate to another world opened in Mikado City, and invaders called Neighbors appeared.