Yifay consented to having her unborn son genetically altered to produce anti-Borg pathogens. In 2375, when Icheb was still a child, Yifay and Leucon sent him to the Borg in order to infect them with the pathogen. In this manner, Yifay and her husband hoped to stem the tide of Borg invasions that were devastating their world.
Icheb returned to his parents a year later, having been rescued by the crew of the USS Voyager. However, as soon as Voyager left, Yifay and Leucon forcibly sedated Icheb in preparation for sending the boy to the Borg again.
Fortunately for Icheb, Voyager crewmember Seven of Nine had had her suspicions about Icheb's parents. She successively collected evidence against them, and Voyager went back to investigate. They interrupted Icheb's parents' plan and saved him from being reassimilated. Icheb remained permanently on Voyager until they reached the Alpha Quadrant. It is unknown what happened to Yifay after Icheb was rescued the second time. (VOY: "Collective", "Child's Play")