Shel-la and his group, as well as Zlangco's Nol-Ennis faction, were exiled to a moon in the Gamma Quadrant by his homeworld Tevlin-De's leaders for not finding a way to stop their long-running war. As an additional punishment, Tevlin-De's leaders created nanite-like bio-mechanical microbes that resurrected people after death, forcing the Ennis and the Nol-Ennis into an eternal war. Shel-la and his people died countless times over decades and were always resurrected and healed of their injuries. (DS9 episode: "Battle Lines", DS9 novel: Rising Son)
In 2369, Shel-la encountered Benjamin Sisko, Kira Nerys, Julian Bashir and Opaka Sulan when their runabout crashed on the moon. On their urging, Shel-la offered a truce to Zlangco as Bashir was close to finding a way to disable the microbes. The cease fire was unsuccessful and Sisko decided not to give Shel-la the data on how to disable the microbes, as Shel-la was more interested in finally killing the Nol-Ennis than leaving the moon and dying permanently. (DS9 episode: "Battle Lines")
Over the next several years, Opaka served as a negotiator between Shel-la and Zlangco. In 2372, she mediated a cease fire that lasted several days. Although it did not last, it marked the end of the fighting. The two factions were later united, becoming known as the Sen Ennis.
In 2373, Shel-la took several people to look at the Ascendant Raiq's crashed ship. After Raiq recovered, Shel-la and Zlangco allowed Opaka to meet with her as their leader. Shel-la and the others were later able to leave the moon, as Raiq destroyed the satellite network, disabling the artificial microbes. (DS9 novel: Rising Son)