Ai Kitora/Plot

Background
When she was in B-Class, 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-Class member of Border. She was trained by Karasuma in the past, just like Osamu is now.

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 embarassed, 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 neighbor 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 Kazam, both side have different reactions, with Kitora feels relieve for their successful mission. Izumi then expresses his disappointment, only to be mocked by Kitora.