Kes becomes non-corporeal
A non-corporeal lifeform was a species composed of various forms of coherent gas or energy. (TOS: "Wolf in the Fold", "Errand of Mercy") Some non-corporeal entities absorbed and utilized energy directly from their environment. (TNG: "Lonely Among Us"; ENT: "Zero Hour")
Others, such as Redjac or the Beta XII-A entity, derived sustenance from the emotions of humanoid lifeforms. The dikironium cloud creature of Tycho IV forcibly extracted the corpuscles of iron-based blood and fed on that. (TOS: "Wolf in the Fold", "Obsession", "Day of the Dove")
Generally, non-corporeal species did not utilize technology, compensating with intrinsic physiological capabilities. Some non-corporeal races had apparently evolved beyond the need for sustenance, and wielded substantial control over space and time. (TNG: "Encounter at Farpoint")
The planet Meridian and its inhabitants spent sixty years in a non-corporeal state. (DS9: "Meridian")
During the original Enterprise NX-01's mission, the crew encountered a species referred to as "Wisps." They had the ability to take over the bodies of humanoids, one notable exception being Doctor Phlox. (ENT: "The Crossing")
In early 2374, Kes became a non-corporeal lifeform after USS Voyager's encounter with Species 8472 in the Delta Quadrant, and the growth of her telekinetic, or psionic abilities. (VOY: "The Gift")