Unlike her peers Belial was a timid and fair woman. She had incredible talent for magic and a strong protective spirit. Her compassion was her curse. Being a student of Raum, Belial saw the power her master and his acquaintances were playing with. Belial was Raum's best student and she had an uncanny skill at deciphering magic. Her talent for unraveling the complex strands of information woven into the casting of a spell and/or the creation of an effect, was unmatched by any member of the order and perhaps only surpassed by the legendary Founders. Her talents caught the eye of Raum and he invited her into the Order, despite the protest of certain members. Her motives for joining stood out among the others and she would have to hide them by showing unwavering loyalty and exceptional work. She resolves the best way to stop them is by joining them.
As a member of the Order she leads in the creation of what would become the plague vampire disease. Her talent for understanding spread beyond magic as civilization developed. She became an adept chemist with the goal of understanding her knew physiology and hopefully finding a cure. Her secret quest for a cure to vampirism using scientific means lead her to isolating the physiological changes in the body of a vampire that the curse induced. Unfortunately, she was never able to work out a cure with this knowledge and instead, her research was used to create a virus that could induce the host with a distorted vampirism. This vampirism would become known as Plagued Vampirism, and it came with it's own strength's and weaknesses.
The Bloodborne are a self-appointed family, the survivors of Belial's fall, who have banned together with a unifying purpose. When Belial was slain, all of her descendant's were freed from their curse. The cursed who had "lived" well beyond their natural lifetime were immediately reduced to piles of ash. Those who had been turned in this lifetime and were less influenced by the lives as the living dead, were set free from their curse and offered another chance at life. Some of these thankful individuals were strong enough in their conviction that they gathered their "Freed" and took on the surname, Bloodborne. These Bloodborne had access to the mounds of wealth achieved through their lineage's timeless exploits and with that laid the foundation for a powerful clan. They needed to protect themselves from the wrath of the Order, as they were now humans who held the secret's of the vampires. Luckily for them Belial had known of her inevitable demise and made preparations for such, her secrets left with only a select few of her "children". These final gifts allowed for the Bloodborne to maintain relative safety and begin a small pushing back against the Order.
Belial's Gift was the unfinished, cure she had been working on. Though it couldn't revert the turned back to life, it could prevent the freed from ever going back. As such all those who share the blood of the Bloodborne have a resistance to being turned.