Kaina Tsutsumi/Synopsis

History
When she was a young girl, the president of the Hero Public Safety Commission invited her to join the agency. With a bright sense of optimism at becoming a great Pro Hero, she accepted. For years she was trained conscientiously until she became really skillful with her Rifle Quirk, becoming not only a popular hero but also the best marksman in all of Japan. Her skill and precision with her shots was admired and envied by the likes of Snipe and other heroes with long-range Quirks.

However, the Commission primarily used her for classified missions, secretly disposing of Villains planning to commit acts of terrorism and corrupt Heroes seeking more fame and fortune. At first, she carried out these orders efficiently and without question, but over time the stress of the seemingly never-ending string of murders began to get to her, all the while needing to keep the front as a public Pro Hero. One day, she came across a group of kids who wanted to shake her hand, leading her to hallucinate her completely bloody hand, and resulting in her questioning her purpose as merely just a cog to maintain the phony illusion of their society.

Lady Nagant's disillusionment came to a breaking point when the then-President of the Public Safety Commission ordered her to make two corrupt Heroes who were taking advantage of the system "go missing". She expressed her reservations about the order, questioning whether the lack of transparency was akin to brainwashing. When his insistence on the act's necessity failed to convince her, the President gave Lady Nagant a veiled threat. This proved to be the last straw, with Lady Nagant killing him in response. She was promptly arrested and incarcerated in Tartarus: the Commission covered up the nature of her arrest, claiming that she killed a fellow Hero in an argument instead.

Paranormal Liberation War Arc
Within hours after the end of the Paranormal Liberation War, Tomura Shigaraki, possessed by All For One, started an assault on Tartarus with his accompanying Nomu. Inside the prison, an EMP attack shuts down Tartarus' monitoring system, and ends up freeing all of its inmates, including Lady Nagant. As the inmates start attacking and killing the guards, Lady Nagant makes her escape, noticing how the system isn't responding to their Quirks, before noticing that an inmate banging on his door, unable to escape. Lady Nagant uses her Quirk to open the door, and out come rushing is Kai Chisaki, desperate to reach out to his boss.

Shortly after the breakout, Lady Nagant is approached by All For One, who is honored to meet the traitor of the heroes. All For One asks Lady Nagant for a favor, considering her to be leagues above the other escapees. He explains that a boy would be certain to leave U.A. High School, so he wants her to capture and bring the boy to him. Lady Nagant interrupts, insisting that she has no interest in anything but escaping Tartarus. All For One convinces her that so long as the boy lives, the collapse of hero society she sought will never arrive, so she reluctantly accepts his proposal.

All For One notices the mentally broken Kai muttering about his boss, and asks if he's a friend of hers. She denies this, but sees use in Kai's broken state, so she brings him with her. To seal their deal, All For One offers a gift, and transfers Air Walk to her.

Villain Hunt Arc
One night on a rooftop, Lady Nagant, accompanied by Kai, fires a bullet and hits Izuku Midoriya's phone using a sniper rifle protruding from her right elbow. With the phone pinned to a nearby wall, Lady Nagant talks to Izuku through a microphone inside the bullet. She tells him that if he complies, she will keep his limbs intact. Izuku then moves, prompting Lady Nagant to fire at him. As he is avoiding her shots using Blackwhip, she curves a bullet and lands a hit on Izuku, although he figures out her location and makes his way towards her.

While retracting her rifle, Lady Nagant notes that this is the first time anyone has deflected two of her bullets. Kai then blankly mutters that he wants to get back to his boss. Annoyed, Lady Nagant picks him up and tells him to hide, and begins having second thoughts about bringing him along. Using Air Walk, she goes to finish her mission.

Lady Nagant swiftly moves through the air and shoots two bullets at Izuku from different angles, with one getting deflected and the other grazing Izuku's stomach. As she shot once more, Izuku unleashes a massive smokescreen, catching her off guard. Now knowing that Izuku has multiple Quirks, she repositions up away from the smoke, aiming at Izuku again. She shoots at moving figures, only to learn that they are decoys. She tells Izuku that he can't hide in the smoke for long, but is surprised when he charges out of a building and grabs her arm.

As Izuku asks why Lady Nagant works for All For One, she punches Izuku and he fell through the sky. Lady Nagant responds by telling him about the dark side of the hero society, and how she killed the president. Izuku became shocked, as he thought Lady Nagant killed another hero in an argument, not a president. Lady Nagant told Izuku that he's ignorant, that a superpower society is an illusion and bringing back the status quo will have history repeat itself. Admitting that he was ignorant, Izuku understands why many things in the world are shades of gray and exactly why he helps people as a hero.

Lady Nagant, unconvinced by Izuku's resolve, decides that she needs to distract his focus, so she points her rifle at Kai Chisaki, who was on top of a nearby building, seemingly preparing to shoot at him.