The Sorinar were the accursed Inar, which came to be known as vampires among the common folk.
The Curse
As the Luinar people began to gravitate more toward a nocturnal existence, they discovered that they could access the Moon Lay via Ghost Rings. These were known as Moontreaders. Some of these were even more ambitious, however, and wanted to go beyond just the Moon Lay. They attempted to access the Celestial Lay in the hopes that they could become godlike. Instead, they mistakenly accessed the Shadow Lay, where they garnered the immediate interest of the Fouled Seven, who were imprisoned there. Recognizing that they could steal some of the inar vorsys, the Seven conspired to manipulate the luinar visitors into bringing more of their kind, among other creatures, which they would plan to harvest vorsys from. The Seven believed that with enough vorsys they would have the power to escape the Shadow Lay. But they could not take all of the luinar vorsys, as they needed to be able to return to the material plane in order to bring them more subjects to harvest.
As a result of this loss of vorsys, the luinar changed. They were confined to darkness, and the sun would harm them. Their skins became pale. They maintained their extended life spans as usual, though they were somehow...lessened, more of the Shadow Lay than the material. They walked the world almost like the undead.
To compromise and keep the luinar satisfied and amenable, the Seven bestowed upon them otherworldly powers, such as unnatural strength and speed, as well as the gift of persuasive charm. They felt less pain, and could see in total darkness. Their other senses were heightened. The Seven wanted them to be exceedingly compelling so as to attract more who could serve as a source of vorsys, so they also gave them exceptional beauty (it should be noted that the more a mortal accessed the Shadow Lay, the more they began to transform). These luinar also did not need to eat as they had previously, as their vitality was somehow different, but hey noticed that with no consumption, they began to slip away from the Material Lay. They discovered that simply consuming blood forestalled that process, and some say that the particular craving of blood could be traced back to the those who had been harvested by Anagas (as opposed to one of the other Seven).
Their appearance also began to change. Each one would slowly begin to take on the appearance of the demon who had harvester their vorsys in the Shadow Lay. For example, some became more batlike in appearance (perhaps the most common) as Anagas was known to be more aggressive in this regard. Some Sorinar who were further along in their transformations were given further abilities by the Seven to enable them to mask their new forms with something more akin to what they had looked like before. They could essentially change between forms at will, though they would lose even more of their essence in the process.
Rivalry
The sorinar immediately assumed that their druinar cousins of the Emra Gohg would be eager candidates, but they were mistaken. While the Emra Gohg were jealous of their relationship and access to the Fouled Seven, who they worshiped, they did not like that the change would make them less susceptible to pain, which they regarded as sacred.