This is one of the two scenarios of human evolution in the Rootworld - a headworld that belongs to NarratedByFate.

Transcription:
"Nomarii are creatures born from a desperation of man and the mercy of nature."
"Their purpose is unknown, yet humans discovered they can use them as an armor. Nomarii don't feel pain, they aren't even living creatures, more like embodiments of spirits."
"Nomarii have several stages of their armor ability. First, second, third and the fourth stage."
"First, when Nomarii is just a little pocketling, the armor is just local, in many cases just tails and an extra pair of arms."
"Second the Nomarii is big enough to envelop the whole human body in an armor, with the same size the original human is."
"Third, when the Nomarii reaches the size needed, the armor reaches a huge size, gains strength and is capable of defending itself from the immerse force of the Empire.
"Fourth, the Nomarii merges with the human body, which ceases to exist in the process. The former human being then continues its life as an evolved creature that combines the qualities of both creatures. (can be controlled by how long one stays in the armor"

(Designs are just examples)