Border Enlistment Arc

The Border Enlisment Arc is the Third arc of the series.

Characters

 * Yūma Kuga
 * Osamu Mikumo
 * Chika Amatori

Triggers

 * Scorpion
 * Eaglet
 * Ibis
 * Lightning
 * Ray-Gust
 * Asteroid
 * Chameleon

Orientation
On Enlistment Day, Masafumi Shinoda briefly explained how their roles were important, and allows Arashiyama Unit to speak. While most of the novice units were excited, one said that the others were simple-minded. They explained that Arashiyama Unit wasn't a powerful team, only a mascot team to Yūma Kuga. Yūma (who is fully aware of Arashiyama Unit's true strenght) then notes that they were probably manipulated to believe that, as they weren't lying. They split up snipers from attackers and gunners. Once they are split up, Jun tells them to look at the back of their hands at a number. The number reveals how long one has used their Trigger, and Yūma got 1000, which is what people usually get. He also explains that to get to B-Class, one must get 4000. There are 2 possible ways to increase your rank, get low times in the fighting exercises, or win a lot of battles.

Attacker & Gunner Colossal Neighbor Simulation Battle
The first test for Gunners and Attackers was to defeat a Trion Soldier simulation within 5 minutes. Some of the strongest members in Border like Ai Kitora managed to do it in very little time. Osamu apparently couldn't defeat the Neighbor within the time limit. After a few rounds, it is Yūma's turn to fight. He goes up against the Neighbor and defeats it is 0.39 seconds! In disbelief, a participant asks him to do it again, which he complies to and defeats it again in even less time! Back with the gunners and attackers, Sōya Kazama approaches them, and it seems that he wants to fight Yūma. Jun explains that Yūma is still in C-Class, but Sōya stated that there was a misunderstanding and that he really wanted to fight Osamu.

Sniper Colossal Neighbor Simulation Battle
Meanwhile, Chika is with the sniper group, where they practice shooting a Colossal Neighbor with Border triggers. Haruaki Azuma notes that her mentor must have absolute faith in her, as she knew that snipers had to run. When she and another sniper are ordered to fire, she makes a big hole in the wall and apologizes. While apologizing for it, she is praised by her instructors and fellow snipers alike.

Osamu Mikumo vs. Sōya Kazama
Osamu accepted the Sōya's challenge. He brings out his trigger, but Sōya uses Chameleon to make himself invisible and then attack Osamu, effectively defeating him 20 times. Osamu asks him to battle him once more. With that, Osamu turns his Trion into small cubes and scatters them across the arena, effectively drawing out Sōya. He uses a Raygust to create a shield, and then uses a Thruster trigger to ram Sōya against the wall. He then uses Asteroid to turn his Trion into a sphere and hit Sōya with it. Sōya's sword impales Osamu's neck, rendering him down, but Sōya's left side is completely destroyed, rendering him down as well.

Battle Stage "City A"
After excelling in the various training activities, Yūma asks Tokieda how he could increase his points. Tokieda says that he could invite a trainee to battle with him, to which he complies. He picks the trainee that was seen before criticizing the Arashiyama Unit. The trainee agrees and comes to him where Yūma easily defeats him 3 times. Meanwhile, Kido is seen with Shinoda and Rindō discussing Yūma. Shinoda states there will be a large-scale Neighbor Invasion. Back with Yūma, he is trying to buy something from a vending machine when his coin rolls away. He looks to see where the coin went when he sees Miwa.

Yūma Kuga vs. Shun Midorikawa
Yūma speaks with Miwa, while Osamu gets asked by various trainees to battle him after learning he tied with Kazama. He agrees to one of them though, and many trainees follow. Ending his discussion with Miwa, he, Yoneya, and Yōtarō, they go to the main lounge where they see Osamu battling a child. The child beat him 10 times nearly effortlessly, and it turned out to be a child prodigy named Shun Midorikawa. In order to save Osamu's reputation, Yūma challenges Midorikawa to fight. Midorikawa accepts, and using Scorpion, he easily defeats him twice. However Yūma then starts defeating him almost effortlessly.

Explanation of the Neighbor World
Jin appears, stating that Kido and the others would like to speak with Yūma and Osamu. Midorikawa starts dancing around Jin, and Yoneya explains that Jin saved Midorikawa from Neighbors in the past.