The Gargantuans are the main factor of success for the Steam Missionary and its Steam Revolution. For centuries; the people of the Lands waged battles with these mysterious titans. They seem to serve no real purpose other than to roam the plains aimlessly.
Before the ways of the Missionary; it would take 2 dozen horse riders with whaling spears to take a Gargantuan down.
The Steam Missionary spent countless years dissecting and understanding the inner workings of these titans- and soon were able to render portions of their bodies as modern fuel. Their outer fat was pressed and preserved to create the now indispensable Bio Liquid for all human machines; including Executioner Knights. Their inner skeleton; taken apart and smelt with various metals to create Super Metals.