Eidolon

Eidolons are creatures that live within Spirakai.

The exact nature of eidolons is unknown. Sages believe that they are guardians of the dead, hence their strength and the reason they occupy Spirakai. It is further believed that some folks transmigrate into an eidolon if their life has had great worth.

What is known is that they appear to be immortal and sometimes quite powerful. Eidolons range from the size of a common house cat to the immensity of a castle. Summoners make pacts with these beings for their own benefit. However, it isn't known precisely what eidolons get from being used much like a tool by a summoner. Still, some will only be bound through violence or being supplicated.