The Psyche (プシュケー Pushukē, Greek: ψυχή, "soul"), or the "Fountain of Life", was the term for the vampires born with the ability to produce blood (such as Karin Maaka). These vampires were also known as Zōketsu-ki (増血鬼, "Blood-producing demons"), contrast to the term Kyōketsu-ki (吸血鬼, "Blood-sucking demons") for normal vampires.
To the vampires, who were born with the endless necessity of blood, the Psyches were seen as a salvation from God. The Braunlichs, who were aristocrats even amongst other vampire families, claimed the possession of the Psyches born from the Armash bloodline. The Edwardses were entrusted to observe the rituals for these "fountains of life". The blood that Psyches provide was also thought to heal vampires from sterility.When the Psyche was taken all of her blood, she would have died, and this was the reason that she had to bear an heir before her death. Theoretically, all of her heirs would have to continue this lifestyle of a slave, or worse, a tool.
Sophia Pistis was the collective existence of all the Psyches that have ever been born and died to this cycle. There might have been some people who tried to save the Psyches from this kind of lifestyle, and Edward Edwards was amongst them. There seemed to have been none of them that ever succeeded.
After Karin Maaka was ceased to produce blood due to, according to Sophia, the first kiss between her and her human boyfriend Kenta Usui, Sophia was released from this cycle of birth and rebirth. She told Kenta Usui that she would be reborn to the first child of his and Karin's, who turned out to be Kanon Usui.