Noboru Koarai/Plot

Background
Koarai joined Border approximately two years before Chika Amatori and Yūma Kuga, following Mako Hitomi's example. He clung to Haruaki Azuma's leg for over an hour before the Sniper agreed to let him join his unit.

Introduction Arc
Azuma Unit presumably took part in the extermination of all Rads in Mikado City.

Large-Scale Invasion Arc
Azuma Unit is deployed by Masafumi Shinoda to prevent the initial wave of Trion Warriors sent by Aftokrator from reaching Mikado City. Border's traps buy them enough time to arrive on the scene. Just as Azuma Unit is about to go support other units after disposing of the Trion Warriors in the area, a Rabbit emerges from a carcass and punches Tsuneyuki Okudera through several houses. Ignoring Azuma's order, Koarai attacks the Trion Warrior, only to be immobilized and have his arms ripped off by the Trion Warrior. After a failed attempt to snipe at it, Azuma opens fire on his screaming teammate himself, causing him to bail out moments before the Trion Warrior could turn him into a cube.

After the end of the invasion, Azuma Unit becomes the recipient of an Excellent Distinguished Service award.

Round Two
Azuma Unit fights a four-way rank battle against Katori Unit, Ōji Unit and Yuba Unit in the day division on February 5.

Round Four
On February 11 Koarai and Okudera discuss whether they should tweak the map for their upcoming match, with Koarai insisting on it being their only way to stand up to higher-ranked units and Okudera protesting that luck is too big and unreliable a factor. Azuma asks them what they agree on, which is that they should prioritize close quarters combat, although flaws in the plan quickly surface. Azuma voices his preference for a simple map and, after Koarai and Okudera propose watching Tamakoma Second's logs, makes sure they remember his tenet about fighting with strategy. Some time later, Koarai floats the idea of tweaking the map again, which Azuma agrees to. They eventually settle on Cityscape B with a snowy terrain.

On Saturday February 15, Koarai and Okudera equip Grasshopper before the match and spawn in the south-east and north respectively. They activate Bagworm and quickly proceed to meet up. When Azuma tells them what enemies he sees, they decide to target Osamu Mikumo. Hitomi recommends they fight Yūma only with the three of them together. Koarai and Okudera launch a sneak attack on Sumiharu Inukai just as he is about to defeat Osamu, cutting off the Gunner's arm. Shinnosuke Tsuji arrives moments afterwards, but the narrow hallway prevents Inukai from supporting him, giving the edge to Azuma Unit. After Azuma successfully snipes at Osamu, Chika forces herself to take a shot at the general location of the four combatants, but they survive. Azuma keeps the two Attackers updated on her position. The two members of Ninomiya Unit however reach her first, but to everyone's astonishment Inukai is taken out by Yuzuru Ema and Masato Kageura before he can shoot her, allowing her to bail out on her own.

The Attackers of all four team are now in the same place, and a battle royale begins. Koarai and Okudera engage Yūma in an airborne battle, focusing on him as he also has Grasshopper. After Tsuji breaks them up, Koarai narrowly avoids Kageura's Mantis. Hiro Kitazoe manages to fire off three rounds of Meteor before Masataka Ninomiya takes him out, wreaking havoc on the battlefield. Okudera is cut to shreds by Kageura and Koarai only barely blocks a slash from Tsuji, only to be defeated by Yūma. Eventually, only Azuma, Kageura and Ninomiya are left, each hiding from the others. Koarai apologizes to Azuma for not scoring any points but his spirits are lifted when the Sniper points out that the snow setting worked out really well.

Galopoula's Blitz
On February 19, the night of Galopoula's blitz, Azuma Unit fights a rank battle against Kageura Unit and Yuba Unit.

Round Seven
During the next enlistment day, Koarai roams the solo rank battles hall with Hisato Sasamori. The two take notice of the trainees' excited chatter and ask Yūta Miura and Kotarō Tomoe what is happening. To their befuddlement they learn that Hyuse went from C-rank to official agent in only a few hours. The four agents propose to fight a five-round solo battle against him each. Excited, Koarai fights first, but he loses all five rounds, as do Miura and Tomoe. Only Sasamori manages to eke out one win, earning Koarai's praise. The latter spots Tsuji and persuades him to try his hand against Hyuse, shocking the B-rank Attackers when he manages to win only two rounds. Koarai notices Tatsuhito Ikoma next, who agrees to spar with Hyuse. The defeated Attackers follow the match with interest, with Koarai betting on Ikoma's victory. However, in the very last round the no. 6 Attacker breaks the rules by using Senkū, which results in his forfeiting the point and decreeing Hyuse's victory. After nagging him for the foul, Koarai looks for more contenders, only for Kei Tachikawa himself to volunteer. Koarai cheers as the no. 1 Attacker wins all rounds but one. After the match, Koarai and the other B-rank agents greet Hyuse, and Koarai invites him to join Azuma Unit. Hyuse however refuses, claiming he has already promised to join another unit.

The members of Azuma Unit then meet up to strategize ahead of their match against Tamakoma Second, Kageura Unit and Suzunari First. In the few minutes before the battle begins, Tamakoma Second is revealed to have added a new member, whom Koarai recognizes as Hyuse. When the map chosen by Suzunari First is revealed to be Cityscape D, Koarai immediately requests Meteor. Okudera and he agree to equip Grasshopper. Koarai disagrees with his teammate about the map being anything other than an anti-Sniper choice. After Azuma tells Okudera to treasure his instinct, Koarai suggests scoring as much as they can early on, but Okudera objects that if they are separated and he runs into Hyuse, he will lose right away, which Koarai begrudgingy concedes. He then states that he does not know if Hyuse will fight exclusively as a swordsman, although his technique is good enough for him to do so. Koarai and Okudera respond correctly when Azuma asks them how they should fight a unit that outnumbers them.

Koarai spawns in the western side of the map, which was given a night time setting. Okudera tells him to meet at the eastern first-floor entrance, and Koarai asks Azuma what he is going to do. The Sniper replies that he will enter the mall too. When Okudera makes contact with Osamu, Koarai rushes to assist him. He climbs to the fifth floor with Grasshopper to cut the Shooter off, but Osamu bulldozes past him with Thruster. Koarai gives chase, unaware that Ema is going to shoot both of them. He is saved by Osamu, who pushes him aside with Thruster one more time. The Attacker falls off the floor, but catches himself with Grasshopper. Suddenly, the lights go off. As Ema shoots off Osamu's arm, guided by his Raygust's glow, Koarai and Okudera sheathe their Kogetsu. Osamu manages to get away and Koarai activates Bagworm as he climbs back to the fifth floor to catch Ema in a pincer with Okudera. He soon gets into position, but Okudera tells him to wait until Ema opens fire. When he does, the two Attackers rapidly converge on him, with Okudera telling Koarai to use Senkū if Ema tries to jump to a lower floor. The Sniper breaks through the railing with the stock of his Ibis, narrowly avoiding their slashes; however, he is shot down by Azuma, towards whom Koarai and Okudera had lured him.

Shortly afterwards, they see Osamu bail out. They close in on Hyuse and Yūma from the south while Azuma approaches from the north. The Sniper also has Hitomi activate the Dummy Beacons he planted earlier. In response Chika fires an undivided Meteor cube at the mall. On top of destroying half of the decoys, the explosion causes Okudera to bail out and injures Koarai's foot. Koarai is bemused by the development, having believed until that point that she was unable to shoot others. Azuma asks Okudera and him what their next move should be. Okudera suggests full retreat, and Koarai reluctantly agrees. He hides with Bagworm, but Hyuse begins to close off all exits with Escudo, preventing the members of Azuma Unit from getting far enough to bail out on their own. After Azuma lures Yūma away with a few Dummy Beacons, he has Koarai lure Hyuse into a trap, resulting in his defeat. Koarai cuts his way out of the mall and asks Azuma what their next move will be. The Sniper responds that it depends on what Tamakoma Second will do. When Chika begins to bombard the mall, Azuma and Koarai bail out spontaneously, ending the match.

The commentators note how Koarai's uncharacteristic decision to retreat could be a sign of growth, although to Koarai, depressed at having done nothing but run away, it does not feel that way. Azuma retorts that both Attackers judged the state of the battle properly, and finally authorizes them to equip Sub Triggers. Ecstatic, Koarai announces his intention to go with Hound.

Round Eight
On March 5, Azuma Unit faces off against Kageura Unit and Ōji Unit in the day division of rank battles. During the match, which takes place in Exhibition Hall, Koarai and Okudera surprise the enemy teams by fighting with Gunner bullets for the first time. Azuma Unit wins the match with a final score of 4-3-3.