A slightly iridescent book with information about the Realms' inner workings in it.
In this book, it is explained how a Realm is created and what goes into the processes of forging a new world. It is updated from time to time as new worlds and their processes are found, watched, and studied.
Realms are forged but rarely, and by First Beings or strong gods. The power needed to create an entirely new dimension is vast, and few gods may harbor it alone. An existing Void hydra must also partake, or the Core will remain unstable and fail, leading to the world's destruction without a corresponding balance. If a vacant Void hydra cannot be found, one that already holds worlds may adopt the created Realm and help in forging a balance.
Depending on the size and element of a Realm's Core, a number of spirits must willingly sacrifice themselves to form the new Ether; at least twenty are needed. Often, a First Being will create these spirits for this very purpose, though gods may harvest spirits from other Realms that exist close enough to tamper with. The strength of a Realm's Core is decided on how strong the spirits aiding creation are, what power the creator(s) put into it, and the strength of the Void hydra helping.
In a Realm's creation, the initial pattern is always the same: the creator gathers souls to help, along with the hydra it is to be bound to, therefore beginning the process. First, half of the collected souls must give up the core of their being in great sacrifice - if done quickly and with a willing spirit, it is painless and undamaging. If not, consequences to both soul and Realm can be dire, and extremely agonizing, until said soul is destroyed. Once the energy and reiatsu are released, it is concentrated into a small orb - the heart of an Ether Spirit. Power fed to that heart by the existing Void hydra causes it to grow and take physical form.
The other half of the sacrificial spirits are likewise harvested, but the orb of their reiatsu is molded by the First Being or god(s) that initiated the process. That is the Realm's Core - heart of the world itself, composed of whatever element(s) it has been centered around. This Core is then taken through a Realm of Light and one of Darkness - such as the Fiv'ean Light and Dark Realms - where those energies focus and refine the Core. Once removed, it is clasped in the jaws or the tail of the Void hydra, and threads of power tied to its heart.
Slowly, the energies form an orb around the Core, encasing the energy inside of it in a swirling mass of reiatsu unique to every Realm. While this takes place, the creator adds the crust and outer covering to the Realm and begins to craft the beginnings of ecosystems and how the world functions, operates, and exists - the laws that allow it to remain alive. After the crust and reiatsu atmosphere are completed, a Veil of magic closes about it and stars are born within the Sphere and Markers are forged to tie it into place, protecting it from the Nothing outside of the Void hydra's protection. The creator, and any gods born or having helped with such a process, then oversee the new world's growth and the creation or adding of animals, plantlife and other aspects of living. Taking life from another, existing planet and adding those species to the new Realm is common practice - as is the travelling between Realms once they are completed.