Fenna was a psychoprojective telepathy projection of the unconsciousness mind of Nidell. Fenna was actually a being of pure energy, a doppelganger for Nidell.

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 frustrated when she wouldn't tell him anything about herself or where she came from. He was surprised when he met Nidell, who appeared identical to Fenna, on the Prometheus. The next time Sisko saw Fenna he called Lt. Dax into 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 mated for life. Gideon said that Fenna had appeared at least once before, and then he came to the realization that Nidell was using Fenna when she was in deep emotional distress. 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 the Prometheus could stop him, Gideon left the ship and was about to commit suicide by colliding his shuttle with Epsilon 119 (re-igniting the star) 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")

Fenna was played by actress Salli Elise Richardson.
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