The Divine Transmigration is the ritual used to ensure the quick reincarnation of the Eternal Suzerain, the draconic demigod ruler of the Sangiran Empire. The ritual was not performed at the death of the most recent incarnation, and the demigod has been missing since.
The reincarnation of the Eternal Suzerain is not immediately guaranteed. Instead, upon death the mortal soul of the Suzerain would enter the cycle of souls, to perhaps eventually make its way back to the Material Plane in another body once again. This is impossible to predict, and the Suzerain could return in any form at any time.
To ensure continuity, every incarnation of the Eternal Suzerain, aside from the last, has performed the ritual of Divine Transmigration instead of allowing the natural movement of the soul to take place. By doing so, the Suzerain and their assistant priests can ensure rebirth will occur nearly immediately and in a specific body. Though not necessarily required, the Suzerain has always chosen to reincarnate in a draconic form, usually by targeting a specific clutch of eggs.
At the passing of an auspicious date, each incarnation of the Eternal Suzerain has performed the Divine Transmigration in hopes of returning in an even more powerful physical form.
The exact details of Divine Transmigration are known only to the Suzerain and the senior-most of their priests - since Y9606*, this information has continued to be passed down within the church.