In the mirror universe, Kira Nerys was the intendant of Bajor's mirror counterpart in the late 24th century. She was stationed on Terok Nor's mirror counterpart and Gul Elim Garak's mirror counterpart was her second-in-command.
Prior to becoming Intendant of Bajor, she served as chief of security for her predecessor, Gul Dukat. While in this post, she helped Dukat conceal his affair with her mother, Kira Meru (ST duology: Dark Passions).
Shortly before her encounter with her primary universe counterpart, Intendant Kira was elected Overseer of the Alliance during a conclave on Khitomer, giving her authority over trade matters and placing her directly beneath Regent Worf. The appointment drew the ire of Intendant Deanna Troi of Betazed, who encouraged First Minister Winn Adami to assassinate Kira. Winn's associates in The Circle hired Annika Hansen to assassinate Kira, unaware that she was an agent of the Obsidian Order. On orders from her superior, Enabran Tain, Hansen revealed the plans to Kira and subsequently assassinated Adami on her behalf (ST duology: Dark Passions).
She related to Kira the story of James T. Kirk's visit to their reality a century earlier and how Spock's mirror counterpart had followed Kirk's advice and began to preach reforms of the Terran Empire, leading to its takeover by the Alliance.
Kira later encountered Commander Benjamin Sisko when he was brought to Terok Nor by Miles O'Brien's mirror counterpart. Believing him to be "her" Sisko, the Intendant was duped by him, long enough for him to convince Jennifer Sisko's mirror counterpart to join the Terran Rebellion. (DS9 episode: "Through the Looking Glass")
After the Rebellion took Terok Nor, the Intendant was captured by them before she was able to escape. Captain Sisko visited her in the brig, and attempted to convince her to tell him a way of delaying Regent Worf's mirror counterpart's ships. She did so, telling him their sensors could be fooled by warp "shadows."
Kira was later captured again - this time by the Alliance - and incarcerated on the Negh'Var's mirror counterpart. She was later able to escape once more, after the cloaking device was sabotaged by Rom's mirror counterpart. (DS9 episode: "The Emperor's New Cloak")