Ai Kitora/Plot

Background
When she was in B-Rank, she rose through the ranks as a Gunner, but started using Scorpion because bullets were too trion-consuming, especially with her low trion. When she was still in high school, she became an A-Rank member of Border. She was trained by Karasuma in the past.

Introduction Arc
She first appears with Arashiyama, responding to an attack on the school. Upon learning that Osamu had breached the rules, she scolded Arashiyama for praising Mikumo and berated Mikumo in turn. Yūma contradicted her by questioning her line of reasoning, saying that Triggers were originally Neighbor's technology. She became embarrassed when she was unable to reply suitably, and this deepened as Yūma continued on with how she merely being spiteful.

Kitora, later on, was sent to 'escort' Osamu to Border HQ, stating that she was there merely to ensure Osamu doesn't run. However, on the way there, a Trion Warrior appears and starts attacking the civilians. In response, she activates her Trigger and goes after it. After she analyzed the Ilgar's path, she climb on top of it by jumping off a bridge and reels herself in by using her Spider. However, as soon as she landed, the Ilgar activates its countermeasure. In the nick of time, Kitora manages to protect herself by activating Shield. She then retaliates by cutting off a piece of its armor and shooting the exposed part. By doing so, the Ilgar activates its self-destruct protocol and starts heading towards the city. She tries to stop it by shooting it but to no avail. At that moment, Yūma assists her by hooking Chain to its underside and pulling it into the river, just in time before it explodes. After she pulls herself out of the river, Kitora questions about what just happened and her inability to stop the Ilgar.

At that moment, she sees Osamu being surrounded by a crowd who thank him for his efforts. This leads Kitora into thinking that Osamu actually wants to be popular. However, this turns out to be false when Osamu tells the crowd that she was actually the one who saved them. As she corrects her judgment, Yūma congratulates her on her success in bringing down the Ilgar. But, she states that it was someone else who did it and she didn't do anything noteworthy. She then goes on to deal with the crowd who are unsatisfied with Border's failure to protect them. After dealing with the civilians, Kitora continues to escort Osamu to HQ via a personnel-only entrance, leaving Yūma behind.

After Border discovered the source of the recent irregular gates, she joins the extermination process alongside her unit.

Black Trigger Retrieval Arc
She is later seen alongside her unit, acting as reinforcement for Jin. When Jin asks her whether she is there because of Osamu, she annoyingly replies that it is simply because she was ordered to.

When the opposite side decide to split their force, she split with her unit to face the splintered force, leaving Jin to face the others. As the fight starts, Arashiyama orders her to protect Satori, who's been discovered after he missed the shot directed at Izumi, from Yoneya. She then faces Yoneya midair with the latter quickly attacks her. Though she manages to block the attack, the force of it knocks her into a nearby building. Yoneya follows suit, taunting her in the process. As they fights, Jin manages to eliminate Kikuchihara. This prompts her to mock Yoneya, who simply brushes it off. Their fight continues with Kitora luring Yoneya into smaller space. She stops after reaching a room, where she lays a trap using Spider. When Yoneya's arm catch the wires, she quickly stabs him, destroying his Trion supply in the process. However, before Yoneya bails-out, he pushes her outside the window, leaving her vulnerable to attacks. Izumi sees this chance and shoots her with Asteroid. Fortunately, Tokieda manages to block the attack before it could hit her, but in turn leaving him open to sniper shot from Tōma. After shooting Tokieda in the head, Tōma then turns his sight towards Kitora and fires another shot. But before he could hit her vital spot, Tokieda pulls Kitora away, causing him to miss and hit her left leg instead.

After she lands on the ground, she apologizes to Arashiyama for her failure. She then helps him in facing both Miwa and Izumi. Seeing that they are in a disadvantage, she suggests to lure their pursuers into a nearby alleyway. As they lie in wait, Arashiyama contacts Satori, asking for his status. When she hears his casual reply, Kitora reprimands Satori by asking him to take things more seriously. Arashiyama then asks Satori to enhance his Radar for 10 seconds. With this, they find out that their pursuers are heading toward Jin. Knowing this, Kitora expresses her concern, saying that it is a trap, which Arashiyama agrees. After devising a plan, Kitora activates her Bagworm and they chase after their opponents with Arashiyama acting as bait. While they focus their attack on Arashiyama, Kitora attacks Tōma from behind using Leg Blade, forcing him to bail-out.

She then joins Arashiyama, facing Miwa and Izumi once again. However, before the fight begins, the sight of someone bails-out in the distance surprises both sides. When they find out that it was Tachikawa and Kazama, both side have different reactions, with Kitora feels relieve for their successful mission. Izumi then expresses his disappointment, only to be mocked by Kitora.

Border Enlistment Arc
During Border Enlistment Day, she and the rest of her unit handles the new C-Rank agents as moderator. As they are changing the venue, she greets Osamu and asks his purpose of joining the Enlistment Day despite being a B-Rank agent. Osamu then answered by saying that he is there as chaperon for Yūma, who then greets her. Seeing Yūma reminds her of the fact that he is a Neighbor, a fact that explains his attitude during their first meeting. When Yūma asks her about the quick way to move to a B-Rank, she replies that it is either getting a perfect score during training or win continuously in rank battles.

After they arrived at the Training Room, Arashiyama explains that they will participate in a fighting exercise against a Trion Warrior. Kitora then mentions that she has gone through similar scenario back when she was a trainee and adds that this will allow them to know their fighting ability. As she watches the flow of the exercise, she commented that it is good to able to defeat the opponent within one minute during the first time. When she asks the speechless Osamu about his record, he is only able to speak a few lines before being interrupted by the crowd's amazement towards a Trainee's record of 58 seconds. Kitora is mildly impressed by this, saying that it was an average record. However, she is speechless when Yūma manages to beat the record after he finishes the exercise by 0.6 seconds. This makes her realize that it was him who beat the Trion Warrior that attack his and Osamu's school. She is highly delighted when Osamu admits the fact.

While she mocks Osamu, Karasuma arrives at the scene and greets both of them. She quickly blushes and starts to act shyly due to his sudden appearance. She then remarks about Karasuma's rare appearance in rank battles and also requests to do practice with him. However, not only Karasuma declined, saying that she's strong enough as it is, he also requests Kitora to teach his pupil, Osamu, after he finds out that she is the same age as him. This revelation only deepens her jealousy over Osamu.

At that moment, Kazama challenges Osamu in a mock battle. This surprises everyone in the room, including Kitora. When Osamu accepts the challenge, Kitora thinks to herself on its futility. As Osamu keep losing a match after the other, Kitora implores Karasuma to intervene and stop the match. She reasons that it was too early for Osamu to fight an A-Rank agent. When Karasuma asks if she's worried about him, she quickly dismisses it. Yūma then adds that the only reason that made Osamu to accept is because to gain experience. Hearing this, Kitora remarks that this is a third-rate way of thinking and says that if he's not doing it to win, he won't gain the knowledge to win. This surprises Karasuma, who praise her for it.

After losing more than 20 times, Osamu asks Kazama for one more round. This makes Kitora to question his decision. As the match unfolds, she made a prediction on Osamu's tactics which turns out to be wrong. When it was announced that Osamu is down, she finds it regrettable but surprised when the match turns out to be a tie. She then stares silently at Osamu when she joins Yūma as Arashiyama congratulates Osamu. When Karasuma does the same, Kitora visibly turns jealous of Osamu but delighted when Karasuma remarks that winning one round after losing 20 rounds would resulted in disqualification. This leads Kitora to happily mocks Osamu, though the latter is confused over the reason why would she be happy.

Large-Scale Invasion Arc
She, along with the rest of Arashiyama Unit, come to save Yūma from Chano Unit. After Arashiyama diffuses the situation, Osamu learns that a Rabbit is targeting Chika and the trainees with her. He rushes to give her support, and Kitora accompanies him. When they reach the site, Kitora begins battling the Rabbit, launching several rapid strikes with Spider and Scorpion. The Rabbit manages to overwhelm her, holding her by the leg. Determined to win, she severs her leg and then defeats the Rabbit, using Scorpion to balance herself. The Rads inside the defeated Rabbit summon three more Rabbits, one of which manages to cubify her. Konami manages to retrieve her cube, and she is de-cubified after the invaders leave.