Border Enlistment Arc

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

Characters

 * Yūma Kuga
 * Osamu Mikumo
 * Chika Amatori

Trion Soldiers

 * Vander (Simulation)

Triggers

 * Scorpion
 * Eaglet
 * Ibis
 * Lightning
 * Raygust
 * Asteroid
 * Chameleon
 * Fūjin (Mentioned)

Orientation
On Enlistment Day, Masafumi Shinoda briefly explains how their roles are important, and allows Arashiyama Unit to speak. While most of the novice units are excited, one comments that the others are simple-minded. They explain that Arashiyama Unit isn't a powerful team, only a mascot team, to Yūma Kuga. Yūma (who is fully aware of Arashiyama Unit's true strength) then notes that they were probably manipulated to believe that, as they aren't lying. They split up snipers from attackers and gunners. Once they are split up, Arashiyama 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 is to defeat a Trion Soldier simulation within 5 minutes. Some of the newer hot-shots in Border like Ai Kitora managed to do it in very little time upon their enlistment. Osamu, however, was unable to 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 in 0.6 seconds! In disbelief, a participant asks him to do it again, which he complies with and defeats it again in even less time! Leaving the balcony, Sōya Kazama approaches them, seemingly wanting to duel Yūma. Arashiyama explains that Yūma is still in C-Class, but who he really wants to fight is 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 accepts Kazama's challenge. He prepares a countermeasure, but Kazama uses Chameleon to make himself invisible and ambush Osamu, consecutively defeating him 20 times. Determined, Osamu asks him to battle once more. Carefully assessing his repertoire, Osamu turns his Trion into small cubes and scatters them across the arena, effectively drawing out Kazama. He uses Raygust's Shield Mode coupled with Thruster to ram Kazama against the wall. He then morphs the defensive trigger around his opponent, sealing him in, save for a small opening where Osamu shoots at point blank. Kazama's sword impales Osamu's neck, rendering him down, but Kazama's left side is completely destroyed, rendering him down as well. With that, the score is 24-0, a tie to end the match.

Yūma Kuga vs. Shun Midorikawa
After excelling in the various training activities, Yūma asks Tokieda how he can 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 speaks with Miwa, about finding his sister. He offers to support him, but Miwa vehemently refuses and goes to the meeting. 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 boy. The boy beat him 10 times nearly effortlessly, and it turned out to be the 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. While Osamu is stunned by the losses, but Yoneya assures him that the tables would change. Yūma then started to defeat him almost effortlessly. The match ends with Yūma's victory; 8-2.

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. As they head to the meeting room, Jin discusses Midorikawa with Yūma. Yūma noted that Midorikawa fought like an unpredictable animal, which is why Osamu found it difficult to defeat him.

At the meeting, Kido asks Yūma for information about the Neighborhood. Yūma then brings Replica out to explain. Replica agrees to do it, but Kido must promise that he will not attempt to attack Yūma. Kido promises, as long as Yūma followed the rules. Yūma did not sense any lies from Kido, so Replica continued to display a map of the Neighborhood, personally compiled by Yūgo Kuga himself, which included many countries. For an invasion, there were 4 countries that were close enough to attempt it; Liberi, the maritime nation, Leoforio, the cavalry nation, Chion, the snow nation, and Aftokrator the military nation. Yūma notes that of the 4, Aftokrator and Chion were the more likely ones to attack as both nations used Ilgars. They respectively had 13 and 6 Black Triggers when Yūma visited them, but for invasion purposes, they would probably only use 1.

Preparing for the Invasion
After the meeting, Shinoda thanks Yūma for the invaluable information. He explains that Yūgo was his superior in the days of Old Border, and that he was colleagues with Kido who knew him for the longest time. He recommends that Yūma become an official member, though Yūma points out that if he were to suddenly advance in ranks, those who did not agree would come forward, especially since he is a Neighbor.

Jin meets Miwa on the roof. When Miwa demands to know what Jin wants, Jin explains that he foresaw Osamu getting into a predicament during the upcoming invasion, and that Miwa would save him. When Miwa denies the possibility of it happening, Jin tells him that he was a candidate for Fūjin, and should Miwa help Osamu, Jin would recommend that Miwa receives it. Miwa still remains in denial, but Jin assures him that he would save Osamu when the time came.