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

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.

Combat-use Trion Soldiers attack when a gate opens in Osamu’s school just outside of the Forbidden Zone. Worried he’s not strong enough, Yuma tries to stop Osamu from fighting back, but Osamu’s determination to save the other students is limitless.

Osamu gets more trouble than credit when he claims to have defeated Trion Soldier Marmod. Really, he’s covering for the Neighbor, Yuma. Kitora, an A-rank Border Agent, is furious with Osamu for stepping out of line… But does she suspect the truth?

Kitora boldly jumps onto the back of Ilgar, a new type of Trion Soldier, while it’s mid-flight and bent on attacking the city below. Suddenly, Ilgar transforms, enters self-destruct mode and plummets toward its target. How will she escape now?!

Yuichi and Osamu's critical mission to investigate the abnormal gate puts a lot of pressure on Osamu. Meanwhile, Yuma follows Replica’s advice and conducts an investigation of his own. The next morning, Osamu and Yuichi have a fateful meeting with Yuma...

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...

A-rank agents Shuji Miwa and Yosuke Yoneya make an assault on Yuma without even asking what happened. Osamu calls Jin to help.

With Shuji's squad singlehandedly defeated, the Border Agency's executives order Yuichi to defeat Yuma and recover the Black Trigger. Osamu worries about Yuichi's impending clash, while a secret hidden by Yuma is slowly exposed.

Jin encourages Yuma to join the Tamakoma branch. Yuma accepts it if he can team up with Osamu and Chika.

Osamu hears from Replica about why Yuma came to this world, and from Chika about her true feelings.

Osamu, Yuma and Chika decide to join Tamakoma branch to go to Neighbor world as A-rank agents of the expedition force. They go into rigorous training from Tamakoma First Unit in order to become A-rank agents.

Commander Kido fears that Tamakoma branch will become too powerful. He orders A-rank agents who belong to the headquarters to take Yuma's black trigger.

The battle between the A-Rank attack unit and Yuichi Jin begins to rage. In the face of top-level agents, Yuichi tries to turn it into a test of endurance. But just as Shiro Kikuchihara gets by him, Yuichi's Black Trigger goes off!

Yuichi finally reveals his "Wind Blade" technique with the Black Trigger. As his battle with A-Rank vets Kei and Soya reaches its climax, the Arashiyama Unit shows up in support and clashes with the Miwa Unit. Who will emerge victorious?!

Yuichi Jin and the Arashiyama Unit repel the enemy. Receiving news of their elite squad's defeat, the Border Agency's headquarters starts to get nervous.

The day of Yuma and Chika's initiation into the Border Agency arrives. Osamu nervously stands by in support, while they draw the scrutiny of their new peers. At that time,

Osamu readies for his practice fight against Soya Kazama. Soya is a symbol of overwhelming strength, while Osamu has yet to land a hit in over twenty battles!

Osamu doesn't know how to deal with his new reputation as "the guy who tied with Soya Kazama". He is soon challenged by one of his fellow agents to a Rank War.

Yuma and Shun Midorikawa's fight begins. Yuma quietly rages over Shun's humiliating public defeat of Osamu. How will he fight against the A-rank vet? Meanwhile, Commander Kido convenes a meeting to prepare for the forecast massive Neighbor invasion.

The Border brass puts together a strategy based on Replica's information about Neighborhood. Meanwhile, Yuichi Jin senses impending danger for Osamu and asks Shuji Miwa for help. A massive battle with the Neighbors is about to begin in Mikado City!

The Neighbors' large-scale invasion finally begins. The invading army of Trion soldierrs is countered with a defense strategy. Just as the battle seems to turn in Border's favor, a new Trion soldier, Rabbit, emerges from a defeated Bamster!

Border seeks a way to counter the new Trion soldier, Rabbit. Yuma prevents Trion soldiers from infiltrating the city, but is mistaken for the enemy and attacked by the B-rank Chano Unit. Meanwhile, an Ilgar Trion Soldier menaces Border headquarters!

Trion soldiers from Aftokrator appear all over Mikado City. Border is forced to divide its forces to deal with their numbers. Chika's C-rank unit is attacked while organizing the civilian evacuation. What is Aftokrator's true goal?

The C-rank units are revealed to be the true target. The battle intensifies as Hyrein sends humanoid Neighbors Enedora and Ranbanein into combat. Osamu fights to give the C-ranks a chance to escape, but Rabbit's merciless attack on Chika continues!