system
A chat on 4chan
human
Going by cross-cultural knowledge the watchers pilot bodies of animals along with whatever living species on earth. Going by the divine rights of kings especially in Mesopotamia the angels were remote controlling bodies of giant humans. The offspring of the kings and human women would be giants but not have the mind/temperament of the angels but rather of their fellow humans at the time which were a bit primitive. There were other genetic abnormalities of the giants back then too looking at Egypt and India where they were part animal, had multiple arms, blue skin, etc. These piloted bodies without a pilot could reasonably be dangerous.
gpt
Attack On Titan lol