Dax and Worf
In the fourth season, Michael Dorn joins the cast of Deep Space Nine as the Klingon character Worf. Perhaps because of her past interactions with Klingons, Dax is fairly flirtatious with Worf. Worf appears at first to be oblivious to this attention, and in the fifth-season episode "Looking for par'Mach in All the Wrong Places" he becomes enamored with a female Klingon named Grilka. This is resolved by the end of the episode, with Quark ironically winning the heart of Grilka, and Worf becoming romantically involved with Dax.
In the beginning, their relationship is very sexual, with the strong implication that their encounters are somewhat rough (the above episode ends with Worf and Dax visiting the infirmary with various bruises and other injuries). In the season 5 finale "Call to Arms", the station is overrun by Dominion forces, and Dax and Worf are assigned to different starships for the Dominion War. Near the end of the episode, they agree to get married after the war is over. Worf and Dax's marriage is the centerpiece of season 6 episode "You Are Cordially Invited...". During the episode, Dax must obtain permission from the lady Sirella to join the House of Martok. At first Dax is loath to pay Sirella the required respect, and the lady is unwilling to accede to Dax's request. The situation is resolved by the conclusion, with Sirella admitting during the ceremony that nothing can stand between "the beating of two Klingon hearts".
Read more about this topic: Jadzia Dax