Kaina Tsutsumi/Synopsis

History
Lady Nagant was a Pro Hero that worked for the Hero Public Safety Commission. Her precision with her Rifle Quirk was envied by the likes of Snipe and other heroes with long-range Quirks. However, she became disillusioned with hero society and sought to bring it down, killing many heroes in the process. She was eventually arrested and incarcerated in Tartarus.

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, and EMP attack shuts down Tartarus's monitoring system, and ends up freeing all of its inmates, including Lady Nagant. As the inmates start attacking and killing the guards, 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. Nagant uses her Quirk to open the door, and out come rushing is Kai Chisaki, desperate to reach out to his boss.

Villain Hunt Arc
Shortly after the breakout, Nagant was approached by All For One, who was honored to meet the traitor of the heroes. All For One asks 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. 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 Chisaki muttering about his boss, and asks if he's a friend of hers. She denies this, but sees use in Chisaki's broken state and claims that he is a victim of hero society, so she brings him with her. To seal their deal, All For One offers a gift, and transfers Air Walk to her.

One night on a rooftop, Lady Nagant, accompanied by Chisaki, 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, C-46 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, Nagant notes that this is the first time anyone has deflected two of her bullets. Chisaki then blankly mutters that he wants to get back to his boss. Annoyed, 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.