Originally, the Delphae were entirely human, and were allies and friends with the Styrics. However, following the events of the war with the Cyrgai (during which the Styrics and Delphae cooperated to decimate the warmongering race), Edaemus and the Younger Gods of Styricum became embroiled in an argument about an unknown issue (and one which, according to Aphrael, was actually rather childish); this argument "spilled over" into the affairs of their respective children, prompting a schism between the two races. With few, if any, attempts at reconciliation, the fighting grew worse and worse, causing a rabid racial hatred to form between the two races (a fate not dissimilar to that between most Elenes and Western Styrics). This prompted Edaemus to take radical action to protect his children- by cursing the lake that was their only source of water, causing the curse to fill and mutate whoever drank the water.
Physically, the curse did little to the Delphae, aside from causing their skin to glow (and possibly causing them to become unusually pale, although this could be a purely racial characteristic). However, the curse apparently caused some sort of accelerated evolution of the soul and mind, and gave the Delphae a variety of magical abilities. One of their most recognizable and feared abilities is the power to touch people and animals (and, with the added invocation of certain spells, plants) and cause them to decay- while still alive. They also have the ability to directly manipulate light, which allows them to achieve some form of personal invisibility and to conceal objects from view without moving or changing them. They also gain an advanced form of telepathy, by which they essentially "absorb" the contents of one's concious mind and file the information within their own mind for later perusal. Their final displayed ability is to change their physical forms (which can include their gender and even their molecular structure); however, if Xanetia is of any indication, the Delphae prefer to manipulate the light and color of their forms, rather than their actual physical makeup.
Despite their reputation as bloodthirsty beasts among the other races, the Delphae are shown to loathe violence and bloodshed and try to avoid violence whenever possible, even showing anguish when they must invoke their curse.
At the end of The Hidden City, the Delphae were shown to turn into beams of light and fly off into space. It is unclear if they retained sentience upon doing so, in which case they may have turned into a form of spirit.