Yōko Katori/Plot

Background
Katori grew up in Mikado City, in an old wooden house left to her family by her grandfather standing right next to Hana Somei's own home. The two are childhood friends, with Somei often visiting Katori during her breaks from study. For her part, Katori put hardly any effort in her studies, but got better grades than her friend. When Somei failed to rank first in her cram school's tests, her father forbade her from going over to Katori's. She thus swapped rooms with her brother and had a window installed so that she could talk to her friend without either leaving their room.

Four and a half years before Yūma Kuga and Chika Amatori joined Border, Katori and Somei lost their homes in the first large-scale invasion. Somei dug Katori out of the rubble, which was trapped under the rubble, rescuing her over her own family because the roof of her house looked lighter. At the hospital Katori found her family safe and sound, while Somei's passed away. Two years after the attack Somei decided to enlist in Border and aim for the top, which prompted Katori to follow her. She started as an Attacker and later switched to Gunner, reaching Master Class in only half a year with hardly any effort, before changing one more time to All-Rounder. For the past two seasons of rank battles Katori Unit managed to stay in the top group of B-rank.

Introduction Arc
Katori Unit was presumably involved in the extermination of all Rads in Mikado City.

B-Rank Rank Battles Arc
After Tamakoma Second's victory in the match against Suzunari First and Nasu Unit on Februray 8, Katori Unit drops to the middle tier of B-rank for the first time in two seasons, later dropping to 9th place when they lose to Nasu Unit.

Katori is on defense duty on Wednesday February 19. After disposing of a Mole Mod she complains that her team is disadvantaged because defense duty prevents them from preparing for their upcoming match against Tamakoma Second and Kakizaki Unit. Rokurō Wakamura tells her to watch the logs before she complains, but she retorts that they haven't lost to Kakizaki Unit in a long time and that Tamakoma Second is not that much of a threat, since it dropped back to the middle tier after fighting in the top one once. Wakamura counters that Nozomi Kako tried to enlist Yūma in her unit, which Katori perceives as a reminder that she herself never got an invitation. The two begin to bicker until they are interrupted by Somei.

Minutes before the match plays on her phone while her teammates look over Tamakoma Second's files. After she makes a nipping remark, Wakamura criticizes her for never making an effort and dropping anything that challenges her. She demeans his skill in turn, but he retorts that precisely because she is so much better than he is, she should stop quitting before even making an effort. Katori rudely dismisses him, and the rank battle begins. She spawns on the west side of Industrial Area, near Yūma, who she immediately attacks. The two clash for a little while without either managing to injure the other. When Osamu Mikumo shoots at her for the second time, she decides to take him out first. As she dashes to him, however, she trips on an invisible Spider wire. Her teammates cover for her before all three retreat. Her actions spark another argument between Wakamura and her.

Tamakoma Second chases Katori Unit into the wire zone, but they manage to escape, only to be immediately confronted and outgunned by Kakizaki Unit. At Somei's suggestion, they move to an open space to force Tamakoma Second to intervene. The three squads separate again. After another brief dispute with Wakamura, Katori advises ignoring Tamakoma Second as long as they stay inside the wire zone. Kakizaki Unit decides to do the same, but before the two squads can engage, Chika begins to bombard their surroundings with Ibis. Not having watched the logs, Katori is momentarily confused. To stop the bombardment they would need to go into the wire zone, so an alliance with Kakizaki Unit is forged. Somei explains to Katori that the other squad is waiting for them to go in first because that way they will be more likely to be targeted by Yūma. However, the one who bars the way is Osamu. Thinking it will be easy to defeat him, the members of Katori Unit advance together, cutting down his wires. Chika's Lead Bullet sniping, however, soon forces them to take cover.

Katori rejoices when someone from Kakizaki Unit bails out, not realizing that the less the squad lasts, the sooner Yūma will join up with Osamu. Yūta Miura suggests taking a detour, but Katori does not want their opponent to set any more wires. She has Wakamura attract Chika's attention while Miura and she go after Osamu. The latter counters with red wires, which Katori recognizes as being for deception, but she trips anyway and is shot in the leg by Chika. She rapidly cuts her leg off while Miura drags her to safety. Faced with this new trick they can't make sense of, Katori has no choice but to recognize that they are pinned in place.

Somei tells Katori to distract Osamu while Wakamura and Miura launch a pincer attack. She does so by talking to him, asking him if he really believes that despite their loss against Ninomiya Unit he still believes that they will make the expedition team, wondering whether he thinks that wanting it alone will get him there. He replies that he simply believes that is what he must do, which angers her. Just then her teammates pounce, but Wakamura is defeated and Yūma arrives on the scene. Katori notices his wound and realizes that if she does not take him out in one shot, the point will go to Kakizaki Unit; this however causes her to freeze up, allowing Yūma to cut off her hand. Miura tries to help her, but he is quickly dispatched by the duo. Katori is reminded of her history with Somei, making her even more enraged. She starts firing at Osamu and Yūma in what appears to be a blind rage, whereas it is a calculated attempt to remove invisible wires between herself and her opponents. She then dashes towards Yūma, but then uses a red wire to change her trajectory, succeeding in beheading Osamu instead. She prepares to confront her last opponent when she notices that she has been tethered to the surrounding containers by the enemy captain right before he bailed out. Before she can free herself, Yūma pierces her trion supply system with Mantis.

The defeat depresses her to the point of wanting to quit Border, as the more she loses, the more she hates herself. Somei tells her to quit if that is what she really wants to do, while Miura understands that part of her anger is due to the fact that she would like to be as creative and hard-working as the members of Tamakoma. She does not feel like she is up to it, but Somei remarks that if defeat upsets her, she has the ability to improve.