One of two factions exiled to a Gamma Quadrant moon, where engineered microbes revive the dead so their war with the Ennis can never end.
The Nol-Ennis and their enemies the Ennis were sent to a moon in the Gamma Quadrant as a punishment. The moon is surrounded by a satellite network and seeded with artificial microbes that repair fatal injuries, so anyone who dies is brought back to life to fight again. Generations of combat have left both sides bitter and unable to stop.
In the episode Battle Lines, Kai Opaka travelled with Benjamin Sisko, Kira Nerys and Julian Bashir and was killed when their runabout crashed on the moon. The microbes revived her, but Bashir found that they had altered her body so that she could not survive away from the moon. Opaka chose to stay and try to bring peace to the two factions.