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!

Aftokrator's humanoid Neighbors are unveiled. These so-called Horn Triggers overwhelm the Border agents with powerful Triggers! The A-rank Kazama Unit uses Kikuchihara's Side Effect in a skillful combo play against Enedora, but will their luck continue?

Kizaki, Karauma and Konami fight the sinister Hyuse and Viza so that Osamu and Chika can escape. Meanwhile, Ranbanein easily defeats Chano unit and takes on Yoneya, Izumi, Midorikawa and Azuma's combined forces. Can Jin's worst case scenario be prevented?

Kizaki has figured out Hyuse's Trigger, Lambiris. He orders Karasuma and Konami to protect the city while he holds off Hyuse and Viza.

Viza and Hyuse continue to pursue Chika, but Yuma and Jin arrive just in time. Yuma faces off against Viza while Jin battles Hyuse. Osamu and Karasuma lead Chika and the C-rank agents to Border HQ. However, Enedora's rampage has the HQ in chaos!

Suwa unit traps Enedora in a virtual training room. Director Shinoda goes to offer them back-up, and the tides begin to turn for Border. Mira's 7 Rabits block the evacuees led by Osamu, as the Aftokrator leader Hyrein heads out to capture Chika!

Hyrein's attack turns Chika into a cube. Osamu blames himself, but is inspired by his fellow Border agents to race for Border HQ in an attempt to save Chika

Director Shinoda corners Enedora in the virtual training room. However, Enedora's powerful Black Trigger attack are more than a match for the Border agents' group attacks. Meanwhile, Karasuma faces Hyrein and activates his true power, Geist!

Karasuma uses his personal trigger Geist against Hairein. He can gain strength and speed, but he has only 200 seconds left to be able to fight.

Miwa uses a trigger Lead Bullet against Hairein. Meanwhile, Yuma decides to carry out a desperate attack against Viza.

Yuma defeated Viza, but he has a few Trion left. Miwa was moved away from Osamu by Mira's trigger. Now there are only seven seconds left until the turning point of the future!

Aftkrator withdrew from our world and the 2nd large-scale invasion is over. Although Chika was saved, Osamu lost conscious. Osamu remembers why he joined Border in his dream.

Osamu becomes conscious, and talks with Yuma after hearing the situation from his mother and Chika. One of higher-ups Karasawa takes him to the press conference by Border.

Many journalists ask the higher-ups of Border about responsibility for damage caused by the battle. Osamu hears about Netsuki's plan from Karasawa, and then he steps forward in front of the journalists and speaks his thoughts.

Yuma and Chika won their first Rank Battle as Tamakoma Second Unit in front of injured Osamu. Their next opponents are the 8th place, Suwa Unit, and the 10th place, Arafune Unit. Osamu can't decide what tactics to use against them.

Osamu recovered and rejoined his unit. Tamakoma Second had the right to choose the location this time, and they chose an urban stage with difference of elevation that snipers like.

The match seemed that it would favor the unit with the most snipers, but Arafune Unit is being driven into a corner by rest of two units. Arafune used to be an attacker, so he launches an attack on Yuma, with a sword type trigger Kogetsu.

Tamakoma Second's next opponents are the 13th place, Nasu Unit, and the 9th place, Suzunari First Unit. Yuma gets a chance to challenge the attacker of Suzunari First, Kou Murakami to a solo match.

Murakami's side effect is especially troublesome issue. Osamu thinks about how to prepare for the next Rank Battle.

The Rank Battle started. Nasu Unit takes tactical actions as planned in the storm. However, Chika's sniping changes the whole situation.

The agents have been divided into east and west across the river. On the west side, a three-way battle between the attackers begins.

On the east side, Kuruma and Betsuyaku are at the mercy of Nasu's shooting. Osamu doesn't want them to be defeated faster than him, so he support them. On the west side, Yuma enjoys fighting with Murakami.

Chika breaks the bank of the river by her sniping, and draws the water into the city. Osamu wants Yuma to join him as soon as possible.

Mikumo Squad joins the B-rank upper tier. The fight against the top B-rank squads will be a touchstone for promotion to A-rank. Anticipating this, Osamu struggles with his inability to score a single point on his own and comes to a conclusion.

Start of World Trigger new arc, Toubousha-hen. Unknown Trion soldiers show up at Border HQ. Jin and Tachikawa take them on.

Zeno, a refugee from Elgates, begs Yuma and Osamu to harbor Lilith and him during their stay in this world. With Chika taken hostage, Osamu and Yuma have no choice but to agree. As they return to the Shizuka City retreat, an unseen assassin strikes!