Phasing was the process by which Koturians transformed and took on a new physical appearance during their marriage ceremony, beginning prior to the moment of the ceremony itself. Several internal and external factors caused their metabolism to go into overdrive, primarily the chemicals and neurotransmitters involved in love and bonding with another person, to produce the change. Although non-Koturians were unable to change, a Koturian could still marry a non-Koturian and change, because the act of love was the catalyst for the process.
The process of Phasing was a sacred rite of passage to Koturians: upon marriage, the newlyweds were the first to see each others' new faces as they began their lives together. However, the process only happened once during a short window in the prime of a Koturian's life. Koturians had some control over their new appearance, depending on the will and strength of their love. During the ceremony the bride and groom placed their hands on Imori stones, which amplified their love and allowed the transformation to become complete. (PROSE: Something Borrowed)