Yun was a young female native of an unidentified planet located in the Delta Quadrant who was affected, like the rest of her people, by radiation poisoning due to an accident on her homeworld.
She met Tom Paris, Neelix and Joseph Carey in 2378 when they were taken hostage by the natives. Paris gave her a small toy that played The Four Seasons by Antonio Vivaldi when pressed.
She was the first to notice that her ravaged homeworld had been restored to a healthier state by the crew of the USS Voyager. (VOY: "Friendship One")