"These are not the fallen giants your heroes faced in your stories. Our god emperor preserved these since the eldar times."
Fire giants, not to be confused with the Kerchki, are rage-filled arson-obsessed giants that want to see the world burn. The Kerchki, on the other hand, are eldar fire giants saved by Alerius and Tiamat from the ravages of Time. They joined Morbatten and its purpose and view Alerius as their avatar.
Standing almost 18' tall, the Kerchki can choose whether to be seen by mortal eyes or not. When viewed, they are most often cloaked by illusion magic gifted them by Alerius. Keenly intelligent but obsessed with fire, the Kerchki enjoy finding and harnessing new ways to store and release (destructively of course) heat energy.
They view fire giants as victims of Time and hope that when Alerius ascends as their god, he will be able to bring Consecration to them and re-unify the race as a whole. Because they do not have a racial god or dominion (yet), their involvement in the Tehran world ages them. As such, Alerius has asked that they serve as sentinels, locked away in the River, until such time as a Dar priestess calls them. Later, this was clarified to the Dar clerics of the respective temples and certain other conditions. This is why they did not fight against Orcus in the 1st Cascade. Alerius treasures them, perhaps more than he does humanity. He was only able to save 4,000 from falling. Their leader, Alerius' friend Sar Jorek, became trapped in Merakor in the Kinslayer Wars. To survive, he took command of the giant armies and marched them against Merakor for the dark elves.
When/if Alerius takes the Elemental Plane of Fire, Sar Jorek will become the God of Fire Giants. Until then, they weep to see how far their brothers have fallen. Kerchki do not interact with mortals unless their conditions are met, and then only briefly or when they decide the risk of aging is worth it.
Compared to fallen fire giants... there is no comparison. Even the fallen feel it and unconsciously obey the Kerchki. In Malcor's time, 3,000 kerchki reside in Morbatten and the other 1,000 in Bloodstone as sentinels on the causeways between the fortresses. Most people of the Isles consider them cute names for the giant statues standing watch throughout Bloodstone.