(coexisting on another dimensional plane)
Jadzia Dax was a female Trill soldier of fortune who worked for Benjamin Sisko in the 24th century, for the Klingon-Cardassian Alliance and then the Terran Resistance Forces. She was also Sisko's mistress, and, after Sisko's death, Julian Bashir's lover.
When it appeared that her lover had returned from the dead in mid-2371, Jadzia immediately greeted Sisko with a kiss to show how glad she was that he was alive, quickly followed by a slap to the face for making her think he was dead. She didn't realize at the time that the man she thought was her lover was in fact Benjamin Sisko from another universe. She noticed something was different about him, but he convinced her, including being intimate with her. Afterward, she admitted frustration to Sisko privately with not having gained much through a year of fighting the Alliance. Seeing the Rebellion as a lost cause, she suggests leaving, but Sisko intended to keep fighting.
Later, she was shocked when Sisko ordered her to stand down when Bashir stood up to her. She also agreed with Bashir in killing Jennifer Sisko instead of persuading her, but Sisko and Miles O'Brien argued against it. When she finally met Jennifer, she learned the truth about Sisko. (DS9: "Through the Looking Glass")
Sisko left to his own universe before she could confront him about it. Afterward, she grieved and later pursued a relationship with Bashir. She stayed with the Terrans as they overtook Terok Nor and built the ISS Defiant.
In 2372, when Sisko returned to the mirror universe, Jadzia sought him out and immediately slapped him and pulled a knife on him, warning him to never touch her again. Jadzia later joined her new lover, Bashir, on a mission to delay the Alliance's attack on the rebel-occupied station. They took advantage of problems with the ships' navigational sensors. Later, they arrived back at Terok Nor to engage the ships there and were victorious. (DS9: "Shattered Mirror")