Large-Scale Invasion Arc

The Large-Scale Invasion Arc is the 4th arc of the series.

A New Model
The invasion begins with Trion Warriors attack the city. In the school, Osamu instructs the students to evacuate with the teachers, and Chika and Natsume to help the evacuation. Yūma accompanies him to fight the Trion Warriors. Due to the Warriors having an outwards direction in attack, Shinoda splits the units, and sends Jin and Amō to the northwest. Traps are used to delay the Warriors until Suwa Unit and Kuruma Unit arrive. Azuma Unit and Kuruma Unit both encounter a new Trion Warrior.

The new model proves to be overwhelming, as it constantly counters all attacks against it. It manages to overwhelm Azuma Unit, forcing Koarai to Bail Out. With the intel from Azuma, Replica determines it's a Rabbit, a new model being developed in Aftokrator. It's so powerful that a single A-Class agent would not be able to defeat it. The Rabbit's purpose is to capture Trigger users. Aside from its already-powerful abilities, it cubifies Suwa. Kazama Unit takes over.

While discussing the possibility of the Rabbit being overwhelmingly powerful with Kido, Shinoda declares that he may step in.

Kazama Unit fights the Rabbit, albeit with difficulty. After receiving a hit from it, Kikuchihara manages to determine the strongest and weakest spots. Meanwhile, humanoid Neighbors begin to watch Border's battle with the Rabbits. They discuss the power, the captain, Hairein asserts that "Miden" still didn't show its full ability. Meanwhile, Osamu continues to fight many Trion Warriors, only to be overwhelmed by the sheer number. Replica explains that the elimination of the Warriors would take place one-by-one, endangering the evacuations like with Chika. Before Osamu can take action about it, a Rabbit confronts him. However, Yūma uses his Black Trigger to destroy the new model, despite the implications. However, Chano Unit attacks him, believing him to be a hostile Neighbor. The Rabbit, having not been destroyed, attack Chano, however, Arashiyama Unit saves her. At that point, Trion Warriors attack the HQ, only for Tachikawa to attack them. Osamu asks Shinoda for permission to assist Chika and the other C-Class members. Kido authorizes Osamu's doing so, but not Yūma's, as he may be mistaken for the enemy. Kitora accompanies Osamu.

Reaching the scene, they encounter a Mod Rabbit and a Mole Mod. Osamu battles the Mole Mod, defeating it, and Kitora battles the Rabbit. The Mod Rabbit overwhelms her at first, forcing her to dismember her leg to defeat it. From its body, three Rads come out, and summon three other Mod Rabbits. One cubifies Kitora. The rest attack Osamu and the other C-Class agents, but they are saved by Tamakoma First, Border's strongest unit. Tamakoma First easily takes out the Trion Soldiers sent to capture Chika, but the humanoid Neighbors join the battle.

The Humanoid Neighbors
Lamvanein encounters the B-Class union near the Old Mikado City University and attacks them. Using his Trigger Chelidon, he easily overwhelms them, taking out Chano Unit entirely, and wiping out members of different units. As things become bleak for them, Lamvanein prepares to go support Hyuse and Viza. Midorikawa, Izumi, and Yoneya counterattack him. With information from Kunichika, they manage to get him into a tight space. He does eventually manage to trap Midorikawa inside the building. Midorikawa quickly slashes a fire extinguisher and uses the gas as a smokescreen. He then cuts off Lamvanein's leg, forcing him to be in constant flight. Using the flight to his advantage, he rains down bullets on the teams, injuring quite a few. He decides to take them down one-by-one and has Kuruma as his first target. While flying towards Kuruma, Yoneya jumps down, attempting to ambush him. However, Lamvanein turns over, and shoots at Yoneya. Midorikawa, Yoneya, Teruya, and Kakizaki combine their shields to protect him, and he proceeds to stab Lamvanein. Lamvanein reverts to his normal body, and is retrieved by Mira.

Enedra appears before Kazama Unit. He attempts to use his Trigger to launch sneak attacks, but Kikuchihara's Side Effect renders them worthless. Seeing that his method of attack was ineffective, he acts frustrated, to lure Kazama, who believes he is frustrated. Kazama beheads him, but Enedra reconnects his head to his body with his liquefaction, and then sprouts blades from inside Kazama's Trion body. Due to the extensive damage, Kazama is forced to Bail Out. Enedra taunts Kikuchihara and Utagawa, but Kazama orders them to retreat. Reluctantly, they do so, leaving Enedra disappointed and even hungrier for killing.

Jin greets Yūma who was taking down Trion Warriors with Arashiyama Unit. He informs Yūma of the current situation, and the possible ways the future could turn out. When Yūma asks what the worst is, Jin reveals that it is Osamu's death. To prevent this, they would have to do their part in fighting it.

Kizaki and Karasuma engage in a shootout with Hyuse. While fighting, Kizaki and Karasuma use Viper to distract him, while Konami attacks from behind, only to be blocked by Viza. Konami notes that his Trigger gave her a bad feeling. Viza insists that they move on, so Hyuse uses his Trigger to attach a metal shard to Chika. He then begins to drag her to him remotely. Karasuma attacks Hyuse again, and Kizaki punches Hyuse through his thin shield. Kizaki himself gets shard in his arm, though he manages to deduce that Hyuse's Trigger used magnetism to repel and attract. Kizaki orders Karasuma and Osamu to take Chika away since it was dangerous for her to stay near.

Konami continues to attack Viza, but to no avail, since he is too powerful. He then reveals Trion Warriors to head out of the Danger Zone. Kizaki orders Konami to pursue them, while he handled the humanoids. Jin notices that the situation got more difficult. Enedra uses his Trigger to intrude HQ. He attacks the operator's room, killing a couple of them and injuring some others. Hairein chides Enedra for attacking the HQ, stating that it was not as ordered. Mira asks if she should retrieve him for being defiant, but Hairein says no.

Kizaki fights Hyuse, using traps to attack him. His goal is not to defeat the humanoid Neighbors, but rather to stall them. To finish the battle, Viza uses Organon to cut up his surrounding, forcing Kizaki on the defensive for himself, but he is weighed down by the magnets in his arm. He dismembers his arm, but Viza sends an attack past his shield and defeats him. Kizaki Bails Out. With their opponent gone, Hyuse and Viza use Lampyris to speed to Chika. Karasuma, Chika, and Osamu are at a remote entrance to Border, but it doesn't open since all the doors were locked following Enedra's intrusion. Before Hyuse and Viza can reach them, however, Yūma and Jin intercept them. Yūma fights Viza and Jin fights Hyuse. Viza initially holds an overwhelming advantage over Yūma to his generally more powerful Trigger and greater experience. While Yūma is able to use chains and mock-Lead Bullets to hold him down, he cannot land any devastating attacks on him. Jin fights Hyuse with fairly even progress on both sides. Hyuse brings the battle into a dark underground tunnel to use his advantages of camouflage and invisibility and manages to pin Jin to a wall. Hyuse tries to deliver the finishing blow to Jin but Jin traps him in Escudo.

Enedra proceeds to attack HQ more, but Suwa Unit (which includes a recovered Suwa) responds by shooting at him, aggravating him. They lure him to the training room, which allows Suwa and Sasamori to fight him while immune to his attacks since they can regenerate. Additionally, his Trigger could be analyzed for weaknesses. However, Enedra manages to attack them from the inside with his blades and leave them there so that they couldn't regenerate.

Osamu, Karasuma, and the C-Class trainees head to HQ's doors when they are attacked by several Rabbits. They are initially outnumbered and forced to run until Yoneya, Izumi, and Midorikawa arrive and subdue them. Osamu is pinned down by a Rabbit who can use Lampyris' magnetic shards and cannot deliver an attack strong enough to even slightly damage the Rabbit. Chika then gives Osamu her Trion so he can shoot more powerful Asteroids, and demolishes the Trion Warrior. Seeing how easily a Rabbit was destroyed, Hairein decides the situation has gone out of hand and joins the battle himself.

The Captain Makes His Move
Hairein makes a flashy entrance to the battlefield to lure powerful opponents to him. He easily takes care of Midorikawa due to his Trigger's ability to cubify anything made of Trion, and manages to cubify some trainees. Izumi distracts him to allow Osamu and Chika to flee, but Osamu attempts to take down Hairein with Chika's Asteroid. The attack fails due to its lack of skill, and Hairein cubifies Chika. Osamu takes Chika's cube and runs to HQ when he is attacked by two Rabbits. He is only saved by the timely arrival of Replica, who had been sent by Yūma.

Enedra's Trigger has been analyzed by Border. It allowed him to liquefy and gasify his body, immunizing him to attacks. The gas could be used to enter someone's body and attack them from the inside. However, this left his Trion vitals exposed in shells. To make up for this, he had dummy shells. In order to counter this weakness, Shinoda himself goes to the training room and attacks Enedra so quickly that he has no time to create dummies, and all the dummies are destroyed. This allows Suwa to tag the shell with the Trion vitals. The AC is also turned on to nullify Enedra's gas, however, he shifts position and comes upwind, so that Shinoda would breathe in gas and attacks Shinoda from inside. While it appears he has the advantage, Kikuchihara and Utagawa attack him, having been hiding inside the training room with Chameleon the entire time. Since his weak spot was pinpointed, he is defeated and reverts to his normal body. Mira appears, seemingly to retrieve him. However, she dismembers his hand and takes his Trigger, explaining that he was no longer necessary, and kills him. Shinoda orders Kikuchihara and Utagawa to inspect Enedra's corpse to see if any information could be gathered.

Izumi and Yoneya continue to battle Hairein. They deduce that his Trigger only affected Trion-based objects, so he could not defend against rubble. This revelation is seemingly meaningless since he can endure non-Trion attacks, which included Izumi dropping a building on him. However, this is revealed to have a secondary effect of giving Snipers on the top of HQ a clear line of fire. Tsukimi instructs the Snipers to shoot Hairein as his Trion was being lowered by Izumi. Hairein gets Mira to send Rabbits to them to distract them, but Fuyushima teleports the Snipers out of harm's way while Kazama Unit and Suwa Unit came up to fight. When it seems like they've defeated him, Hairein reveals that he can also absorb Trion. He attacks Izumi, and Izumi is forced to Bail Out, much to Hairein's disappointment. With Izumi gone, Karasuma must fight Hairein. He uses Geist to quickly defeat the Rabbit he was fighting and attacks Hairein. Using his Trigger, he uses his significant offensive boost to outmaneuver Alektor bullets. It is revealed that before the invasion, Jin had informed him that he would be defeated by someone during the invasion, and that he would not be able to save Osamu and Chika. Due to his limitations, he can only use Geist for 3 minutes, which was enough time to allows Osamu and Chika to reach the base. Mira then joins Hairein, though, and uses her gates to have Alektor's bullets hit Karasuma in the back, forcing him to Bail Out, and now Hairein seemingly has nothing standing in his way except for Osamu.

Carrying out the Plan
Osamu and Replica are about 120 meters from the base when Hairein appears before them. Replica sends an extension to the base's entrance to analyze the lock and force it open. Replica has Osamu run through buildings to avoid Hairein's bullets. Mira uses the marker in Osamu's arm to open gates near him and send Alektor bullets after him, managing to partially cripple him. Replica's extension is destroyed by Mira, and Osamu is in the open right in fron of Hairein, putting him into an ordeal. Just as things are getting difficult, Miwa shows up, as per Jin's prediction. Osamu begs Miwa to take Chika's cube, but Miwa kicks him, insisting that Osamu do it himself. He also makes it known that he wasn't there to save Osamu but to defeat Hairein due to his hatred of Neighbors. Miwa attacks Hairein with Lead Bullet, against which Hairein cannot defend. While Miwa fights Hairein, Osamu shoots Asteroid at Hairein, but they are cubified. Having apparently fulfilled something, Osamu runs to the entrance when he is confronted by Mira. To counter her, Replica summons its Rabbit to fight her. As the Rabbit was too large for her to defeat, she is put at a disadvantage, similar to Hairein, who could not cubify Mira. She proceeds to bisect Replica. Replica continues to function, but Hairein sends some animals to partially cubify the Rabbit, decommissioning it. As Replica was bisected, most of its functions were lost, but it still retained the ability to unlock the door.

Yūma continues to fight a losing battle against Viza. The latter's experience is far greater than his own, and so was his strength. All of his attacks were in vain as they could not reach their target. In spite of this, Yūma perseveres. As long-range attacking was hopeless, Yūma takes a different approach, attack him head-on. He uses Chain as a bungee and Boost to throw himself towards Viza. Viza cuts him, destroying his Trion body, but he reverts to his normal body, which happens to be a Trion body. He uses this to use Boost right at Viza, destroying him and defeating his opponent. Soon after this, he rushes off to help Osamu.

Osamu runs towards the base, only to be impaled by Mira's spikes. Hairein sends some Alektor bullets to cubify Osamu, but he deactivates his Trigger and returns to his regular body to neutralize the capabilities of Alektor. Planning to go after Osamu himself, Hairein attempts to use the same tactic he used against Karasuma to defeat Miwa. However, Miwa is aware of this and uses Viper to shoot Hairein and Mira through the window through which they planned on sending Alektor's bullets. With the significant Trion loss, Mira teleports Miwa away so that Hairein would be undisturbed. Osamu continues towards the base, when he is once again impaled by Mira, only this time the damage was to his flesh body and therefore more lethal. Osamu puts his plan into action, which was to throw Replica into the Neighbor's ship. Yūma and Miwa use Replica to find Hairein's location relative to their own while they use their Black Triggers (the Ring and Fūjin, respectively) to attack him. Osamu does what he planned to, and Replica overrides the system and sets it to auto-retreat in 60 seconds. Hairein takes the cube Osamu was holding only to find out it was a substitute that he took when he purposely had Hairein cubify his bullets. With no time to go back for Chika, he has Mira retrieve Viza and the Organon, and heads to the ship himself. He orders Mira to leave Hyuse "as planned". The ship leaves, signifying the end of the invasion, while Osamu lies unconscious in a pool of his own blood.

Aftermath
Osamu is quickly rushed to the hospital.