The definition of a Ren is a machine that is capable of carrying out complex commands. A Ren is fueled by magic, typically Kinetic Magic, and the magic is typically enfused in the structure, instead of stored in a usable source, and is therefore lasts longer.
A Ren is typically made out of ebony, but can be made out of other materials. The Dramer, who typically make such devices, shape the ebony into scales, like on a dragon, or Ra'tun, which overlap, and therefore are both extremely tough, and extremely complicated.
The Ren are manufactured only by Dramer Craftsmen, as their design and use is deemed far too important a secret to ever be allowed leave Rekkan. However, the Ren are often sold to the Nokana Empire, to Tóbh, and to other wealthy areas, usually as novelties, but often as war machines.
The most incredible of the Ren are those that stand completely upright, and act as war machines or servants, performing complex tasks, and understanding commands. Unspeaking, and with no eyes, these can be very unnerving. In times of peace, these are rarely seen, however.
A much more common form of Ren is a insect like creature, called a Gatherer. These small insects have a flat back, and can roll up into a near impregnable ball. They are used as anything and everything. Scaled up, they are used as pack mules, as small creatures, they are used to gather fruit and flowers in Eder Orchards, or even as pets.
Arguably the most important Ren of all time is the Guardian. Mirrored after the Dragon Rekkan, it is 20ft long from snout to tail, and guards the Narrowing, a narrow stream that serves as the entrance to the otherwise impenetrable island of Rekkan. Multiple Guardians have been built, and over the eras their designs have improved. The design of the Guardian is a closely guarded secret, and not much is known about how it is built or powered except by an elite few in the College of Rekkan.