The following content was originally created in this thread on Reddit in /r/bloodborne. All credit for the content of this post goes to /u/Decentralist-, with only minor changes being made to reflect the difference in format.
This article examines real-world mythology that may have inspired elements of Bloodborne's world.
From the earliest human cultures, the mysterious magic of creation was thought to reside in the blood women gave forth in apparent harmony with the moon, and which was occasionally retained in the womb to ’coagulate’ into a baby.
Men regarded this blood with holy dread, as the life essence, inexplicably shed without pain, wholly foreign to male experience.
Most words for menstruation also meant such things as incomprehensible, supernatural, sacred, spirit, deity. Like the Latin sacred, old Arabian words for ’pure’ and ’impure’ both applied to menstrual blood and to that only. The Maoris stated explicitly that human souls are made of menstrual blood, which when retained in the womb ’assumes human form and grows into a man.’
Africans said menstrual blood is ’congealed to fashion a man’. Aristotle said the same: human life is made of ’coagulum’ of menstrual blood. Pliny called menstrual blood the ’material substance of generation’, capable of forming ’a curd, which afterwards in process of time quickeneth and groweth to the form of a body.’ This primitive notion of the prenatal function of menstrual blood was still taught in European medical schools up to the 18th century.
Basic ideas about menstrual blood came from the Hindu theory that as the Great Mother creates, her substances become thickened and forms a curd or clot; solid matter is produced as a ’crust’. This was the way she gave birth to the cosmos, and women employ the same method on a smaller scale. According to Daustinius, ’the fruit in the womb is nourished by the mother’s blood....The menstruum does not fail the fruit for nourishment, till it at the proper time comes to the light of the day.’
Indians of South America said all mankind was made of ’moon blood’ in the beginning. The same idea prevailed in ancient Mesopotamia, where the Great Goddess Ninhursag made mankind out of clay and infused with her "blood of life."
The Bible’s story of Adam was lifted from an older female-oriented creation myth recounting the creation of man from clay and moonblood. So was the Koran’s creation story, which said Allah "made man out of flowing blood"; but in pre-Islamic Arabia, Allah was the Goddess of creation, Al-Lat. The Romans also had traces of the original creation myth. Plutarch said man was made of earth, but the power that made a human body grow was the moon, source of menstrual blood.
The lives of the very gods were dependent on the miraculous power of menstrual blood. In Greece it was euphemistically called the "supernatural red wine" given to the gods by Mother Hera in her virgin form, as Hebe. The root myths of Hinduism reveal the nature of this ’wine’. At one time all gods recognized the supremacy of the Great Mother, manifesting herself as the spirit of creation (Kali-Maya).
I LIKE THIS PART THE BEST
She, "invited them to bath in the bloody flow of her womb and to drink of it; and the gods, in holy communion, drank of the fountain of life -- (hic est sanguis meus!) -- and bathed in it, and rose blessed to the heavens".
So there you have it, From Soft does their homework when it comes to mythology and specifically, the blood mythology of Europe from the later middle ages.
Lore Hunter's Note: The following information is additional information provided by the same source in the comments.
The esoteric secret of the gods was that their mystical powers of longevity, authority, and creativity came from the same female essence. The Norse god Thor for example reached the magic land of enlightenment and eternal life by bathing in a river filled with the menstrual blood of ’giantesses’ -- that is of the Primal Matriarchs, "Powerful Ones" who governed the elder gods before Odin brought his ’Asians’ (Aesir) out of the East. Odin acquired supremacy by stealing and drinking the ’wise blood’ from the triple cauldron in the womb of the Mother-Earth, the same Triple Goddess known as Kali-Maya in the southeast Asia.
Odin’s theft of menstrual magic paralleled that of Indra, who stole the ambrosia of immortality in the same way. Indian myth called the sacred fluid Soma -- in Greek, "the body", because the word’s eastern root referred to a mystical substance of the body.
- Soma was the object of so much holy dread that its interpretations were many.
- Soma was produced by the churning of the primal sea (Kali’s ’ocean of blood’ or sometimes ’sea of milk’).
- Or Soma was secreted by the Moon-Cow.
- Or Soma was carried in the ’white pot’ (belly) of Mohini the Enchantress.
- Or the source of Soma was the moon.
- Or from Soma all the gods were born.
- Or Soma was the secret name of the Mother Goddess and the active part of the ’soul of the world’.
Soma was drunk by priests at sacrificial ceremonies and mixed with milk as a healing charm; therefore it was not milk.
Soma was especially revered on Somvara, Monday, the day of the moon. In an ancient ceremony called Soma-vati, women of Maharastra circumambulated the sacred female-symbolic fig tree whenever the new moon fell on a Monday.
Some myths claimed the Goddess under her name of Lakshmi, "Fortune" or "Sovereignty", gave Soma to Indra to make him king of the gods. His wisdom, power, and curiously feminine capacity for pregnancy, came from Lakshmi’s mystic drink, ’of which none tastes who dwells on earth.’ On drinking it straight from the Goddess, Indra became like her, the Mount of Paradise with its four rivers, "many-hued" like the Goddess's rainbow veils, rich in cattle and fruiting vegetation.