Kira was formerly in command of the Alliance space station Terok Nor, with her second in command Elim Garak. Kira ruled over the station with an iron fist, but used varying methods to do her job. She was manipulative where necessary, but incredibly ruthless and excessively violent on other occasions, often rounding up Terran slaves and executing them randomly. She did, however, often view certain people with a strange affection, allowing them privileges in return for their loyalty and dedication. When the Kira Nerys from this universe arrived in hers, she was bizarrely enamoured with the idea of there being two of her.
She was particularly fond of Benjamin Sisko. She allowed him to have a ship and a crew, which he used to commit acts of piracy in order to collect tribute for her. She was horrified when Sisko turned against her and formed the Terran Rebellion. (DS9: "Crossover") When he returned to the station to rescue Jennifer Sisko, Sisko used this fondness to manipulate Kira in to allowing him to see her. (DS9: "Through the Looking Glass")
Kira was captured by the rebels in 2372 and tortured for information, but escaped from their custody having manipulated Nog in to helping her escape, killing him shortly afterwards. (DS9: "Shattered Mirror")
By 2375 Kira's failure to stop the rebels had resulted in her being forced to bargain for her life. When Zek made the mistake of visitng the mirror universe to open trade negotiations, he was quickly captured. Kira arranged for Ezri Tigan to go to this universe and force Quark and Rom to deliver a cloaking device. After Rom sabotaged the cloak, leaving the ship defenceless against the Defiant, Kira was able to escape. (DS9: "The Emperor's New Cloak")
Given her relationship with Ezri Tigan, and her other activities, it seems that Kira is bisexual.