Kōtarō Suwa/Plot

Background
Suwa joined Border three years before Yūma Kuga and Chika Amatori. On one occasion he got Sōya Kazama so drunk that the latter picked a fight with a postbox.

Introduction Arc
Suwa Unit presumably takes part in the extermination of all Rads in Mikado City.

Border Enlistment Arc
On January 8 Suwa and Daichi Tsutsumi oversee the simulation mode for the new recruits. Suwa is unimpressed with their skills, although Tsutsumi points out that it is only by comparison with a few stellar rookies from past enlistment days. They are blown away when Yūma defeats the simulated Bamster in less than one second. Suwa is surprised to see Kazama challenging Osamu Mikumo. When the latter asks for one more match after his 20 defeats, Suwa comments that he'd rather see Yūma fight, but he ends up following Osamu's tactics with interest and is disappointed when it seems that he lost. He reacts with amazement when it is revealed that the match ended in a tie.

Large-Scale Invasion Arc
Suwa 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. A Rabbit emerges from the carcass of one of the defeated enemies, its armor resisting Suwa's and Tsutsumi's bullets. When Hisato Sasamori is stunned by the Trion Warrior, Suwa covers Tsutsumi as he rescues their teammate, only to be captured and stored inside the Rabbit. When Kazama Unit kills it, they find out that Suwa has been turned into a trion cube. Kazama tasks Tsutsumi and Sasamori with bringing it to HQ.

After some initial difficulties, the engineers succeed in reverting the cubification in time for Suwa to intercept Enedra as he rampages inside the base. His Black Trigger appears to make him immune to damage, but Kazama observes that his trion body must possess a relay center and a supply system and that Suwa Unit's shotguns are ideal for finding them. Suwa and Hisato lure Enedra into one of the training rooms. Just as Enedra delivers the killing blow, Tsutsumi activates the simulation mode, preventing Enedra from causing any more damage. Hisato remarks that as long as the simulation lasts, they will be unable to defeat Enedra as well, to which Suwa replies that their goal is to analyze the enemy's Black Trigger and prevent him from noticing the control panel by the door. One of Suwa's bullets eventually hits a hardened shell. Suwa realizes that it contains Enedra's vitals, but the Neighbor simply creates more to hide it. He then injures Suwa from the inside as he did Kazama before him, allowing the Border agents to discover that he can gasify himself. The gas comes in contact with the control panel, ending the simulation. Enedra destroys the room, but before he can finish off his opponents, Shinoda joins forces with them.

The Director single-handedly destroys all of the shells before Suwa Unit can assist him. However, Enedra removes his vitals from the shell at the last moment and paralyzes Shinoda with his gaseous attack. Suwa and Tsutsumi resume firing at him, hitting the shell and marking it with Starmaker before he can create decoys. When the Neighbor foils Sasamori's sneak attack, Suwa and Sasamori pretend to use the smoke caused by the destruction of his trion body when in reality it is Shirō Kikuchihara and Ryō Utagawa, who had been hiding with Chameleon the whole time, who deal the finishing blow. Suwa is irated by the former's attempt to hog the credit. He then relays Kazama's congratulations to Sasamori. Just then Mira opens a wormhole and, to everyone's shock, cuts off Enedra's hand to retrieve Vorvoros and kills him. Shinoda has a befuddled Suwa call the medical team to salvage the Neighbor's horns. Suwa looks on with unease as Kikuchihara and Utagawa casually search the corpse, noting that it must be ordinary for away squads. He and Tsutsumi are subsequently stationed outside of the base and see the last of the Gates close. After the end of the invasion Suwa Unit is the recipient of an Excellent Distinguished Service award.

B-Rank Rank Battles Arc
On February 1, Suwa and Tsutsumi survive their battle against Suzunari First, defeating the powerful Kō Murakami with their combined firepower and Sasamori's obstruction of the enemy.

Round Two
The following day, three days before their match against Tamakoma Second and Arafune Unit, the members of Suwa Unit gather to prepare a strategy in HQ's cafeteria. Suwa remembers that Yūma is in the former team. While watching the logs of the unit's first rank battle he is astounded by Chika's firepower and the discovery that she is Reiji Kizaki's pupil. He asks Sasamori about his track record against Shun Midorikawa, and the answer prompts him to decide that Sasamori will hold Yūma down while he and Tsutsumi blast away at both of them.

On February 5, when Tamakoma Second's map of choice is revealed to be Cityscape C, Suwa complains around in the unit's room. He concludes that they must charge up the hill before their opponents. He spawns a little east of the center of the map. He and Tsutsumi meet up and reach Sasamori just in time to save him from being sniped by Atsushi Hokari, although they end up being pinned in place. When Tamakoma Second attracts the fire of all three members of Arafune Unit, Suwa and his teammates' don Bagworm and go after the Snipers, with Tetsuji Arafune barely surviving a Suwa's sneak attack. Suwa chases the injured captain, seemingly unaware that he is being lured into Yoshito Hanzaki's range, but when the latter opens fire he promptly puts up a focused Shield to defend his head. He then resumes his pursuit of Arafune, only for Hokari to blow off his left leg, delaying him. When Arafune engages Yūma at close quarters, Suwa sends Sasamori after Hokari and activates his Bagworm to take out both Attackers at once. He arrives just as Yūma cuts off Arafune's legs, but both manage to defend against his fire. As Suwa and Yūma face off an invisible Sasamori immobilizes Yūma, but before Suwa can blow both of them away Chika destroys the houses they are standing on, allowing her teammate to free himself and take out Sasamori undisturbed. Unable to chase his opponent, Suwa waits for Yūma to move in for the kill, anticipating his trajectory thanks to the information gathered by Tsutsumi. However, as he goes into Full Attack, Osamu shoots him while Yūma manages to protect himself. Suwa realizes that he has been baited just before bailing out. His teammates tease him for not scoring a single point. As a result of the match, Suwa Unit drops to 10th place.

Round Four
On February 8 Suwa, Sasamori, and Mitsuru Tokieda walk through the base together when Yūma spots them. He walks over and Suwa and he starts horsing around.

Galopoula's Blitz
On the night of February 19 Suwa receives command of half of the mid-range combatants deployed to counter Galopoula's incursion. When the Idras march towards the base, he instructs the agents under him not to stray from the formation, and then to fall back when the Snipers are no longer able to cover for them. When Kizaki, Arafune, Midorikawa and Shinnosuke Tsuji repel the Dogs and the Snipers are freed up, Suwa resumes the attack on the ground troops. The Trion Warriors retreat out of range, prompting Masataka Ninomiya to request half of the Snipers to move to the ground. After a discussion with Nozomi Kako command of the joint forces is assigned by Suwa, who asks for Ninomiya's guidance. They plan to push back the Idras until they reach Shūji Miwa and Yōsuke Yoneya, locked in combat with Koskero. Suwa Unit takes a frontal position in the assault. An unusually powerful Idra flanks them but draws back as soon as Sasamori intercepts it. Suwa warns Kizaki, whose group is also targeted by a similar Trion Warrior. Despite their best efforts, Suwa and Tsutsumi are unable to hit it. With their formation at risk of breaking, Suwa sends Sasamori to take down the unusual Idra. When Yūichi Jin tells Ren Tsukimi to broadcast to everyone that the battle will end soon, Suwa tells Kizaki and Kyōsuke Karasuma to pull out all the stops. Suddenly faced with overwhelming firepower, the enemy moves towards the city with a few Dogs, but thanks to Jin's foresight the Border agents see through his deception and decide to ignore him, with Suwa thanking Shinji Fuyushima for the contingencies he sets in place before turning back to the remaining Idras. After the enemies retreat, Suwa, together with the rest of the ground forces, remains inside the security zone for a while. He notices the slime on Miwa and Yoneya's persons, with the former explaining that they want to take it to be analyzed.