While Nidell and her husband, Gideon Seyetik, visited Deep Space 9 on the USS Prometheus in 2370, Fenna appeared on the Promenade where Benjamin Sisko noticed her and took an interest in her. After several evenings meeting with her on the Promenade, Sisko fell in love with her but became frustated when she wouldn't tell him anything about herself or where she came from. He was surprised when he met Nidell on the Prometheus who appeared identical to Fenna. The next time Sisko saw Fenna he called Lt. Dax in the room. Dax immediately scanned Fenna and found no life signal, only energy. Sisko and Dax took Fenna to Gideon and it was discovered that Fenna's manifestation was killing Nidell due to the extreme stress of projecting Fenna.
Desperate to do anything to save his wife, Gideon confided in Sisko that unlike his other wives, Nidell would never divorce him because her species mates for life. Gideon said that Fenna had appeared at least once before, and then he came to the realization that Nidell was using Fenna to be unfaithful. Privately, Sisko convinced Fenna that she should stop fighting for her own existence in order to save Nidell's life. Fenna told Sisko goodbye and that she would always love him, and they kissed. Meanwhile, before the crew of DS9 could stop him, Gideon had left the station and was and about to commit suicide by colliding his ship with a planet (and terraforming it) in order to set Nidell free. After Gideon's death, Nidell woke up and Fenna disappeared. Nidell claimed to have no memory of Fenna's activities when she asked Sisko, "What was she like?". Sisko replied, "She was just like you", and watched her walk away. (DS9: "Second Sight")