The Oblivion

The Destroyer is the final boss from Romancing SaGa 3. It is the embodiment of the Abyss's power, born when the two destined child, Sarah and Shonen, enter the Abyss at the same time. Sarah warns the heroes that such power would destroy the world, including the Abyss, so the heroes argue that if this power was so great, it could restore the world as well. The heroes tell the the two to combine their strength to convert the Destroyer into a power of creation, while they fought it.

As the Destroyer is defeated, it's power engulfs the world (and possibly the entire universe) and completely annihilates it. However, since it's power was turned into a power of creation, the world is recreated shortly after, without the presence of the Death Eclipse or the Abyss, allowing everyone to finally live in peace.

Other Forms
During battle the Destroyer will take on five different forms or less depending on what is done before facing it. If all the Abyss Lords are not defeated then the Destroyer will be much stronger and have twice as much HP as it will take on the forms of the abyss lords during the fight and use all of their abilities. If all of the Abyss Lords are beaten before facing it then it will only use one alternate form and be less stronger than if the Abyss Lords were skipped.