A fundamental transformation — reborn from the bones up.

The origin of "exchanging the bones, taking a new womb" lies in the Daoist tradition of cultivation. In Daoism, transforming the bones of an ordinary mortal into the bones of an immortal through practice was called "exchanging the bones" (換骨). The man who established this idea as a literary term was the Song-dynasty monk and poetry critic Huihong (惠洪, 1071–1128). In his Notes from a Cold Studio (冷齋夜話), explaining the compositional method of the poet Huang Tingjian (黃庭堅), he introduced two techniques: the "bone-exchanging method" (換骨法) and the "womb-taking method" (奪胎法). The bone-exchanging method takes the meaning of an earlier poet but changes the words entirely; the womb-taking method takes the words of an earlier poet but changes the meaning entirely. In other words, the literary sense of the phrase was "to recreate a master's work anew, down to its very skeleton." The two ideas fused into the single four-character expression, which later broadened into the general sense of "a person becoming completely transformed."

The ancient Greek word μεταμόρφωσις (metamorphōsis) is made of two parts: μετά (meta, beyond / change) + μορφή (morphē, form / shape). Translated literally, it means "what lies beyond form, the transformation of form." The work that engraved this word into Western civilization was the epic Metamorphoses (c. 8 CE) by the Roman poet Ovid (Publius Ovidius Naso, 43 BCE – 17 CE). Spanning fifteen books and some 12,000 lines, it gathers roughly 250 transformations, running from Chaos to the deification of Julius Caesar — Daphne turning into a laurel, Narcissus into a flower, Arachne into a spider. The word entered English in 1533; according to the OED it first appeared in a translation of a work by John Gower. Later, as sixteenth-century natural philosophers used "metamorphosis" for the transformation of insects — from caterpillar through chrysalis to butterfly — it took root as a scientific term as well. In the twentieth century, Franz Kafka's novella The Metamorphosis (Die Verwandlung, 1915) extended it into the realm of psychological and existential transformation.