Fear the Great is an emergency system that activates when malice on a certain planet exceeds a certain level. In Disgaea 4: A Promise Unforgotten, this system is activated at the end of Episode 9 when Nemo's malice activates the system. Archangel Flonne explains that every planet is equipped with Fear the Great and by an order from God, Fear the Great activates and possesses the person with the most malice(in this case, Judge Nemo). It will continue to absorb malice until it destroys the planet it is activated on.
It serves as the main setting for the Final Episode in Disgaea 4 where Valvatorez decides to go to Fear the Great in order to stop it. The dimensional path to it can only be opened by a being of light as Flonne opens it for them. Inside, it takes the place of another dimension with many gray platforms and paths with foreign writing. This place is also home to Malice enemies which take the appearance of one of the classes in the game except with a black and gray palette and no elemental weaknesses.
Lastly, Nemo's only special is named Fear the Great where he flies up into the air with many spheres of dark energy swirling around him. One of these spheres transforms into a planet where a giant Nemo appears to the enemies affected before sending a dark energy sphere to blast them. The rest of the dark energy spheres bombard the planet, one by one, before Nemo bombardsthe planet using them all, making it crack at first and then shatter completely.