Zeromus is another villain I never really thought much of. At a literal level, Zemus is a bad guy on the moon who mind controls people so he can carry out his scheme of destroying the Earth. Then when he dies, Zeromus rises from his corpse and goes "MUWAHA I am Zemus's hatred! I'll kill you all, fools!"
Sure. That might as well happen.
The thing about Final Fantasy IV is that it's a game that is begging to be examined through a metaphorical lens, moreso than a literalistic one.
The King of Baron was a good man who raised Cecil and Kain with good values but then one day he was secretly killed and replaced by a grotesque monster dressed in his skin. This creature wages war on other countries in the name of hatred.
At the literal level, Cagnazzo is not himself the man who raised Cecil and Kain. But this is a symbolic transformation, the death of the man they loved as he instead becomes a disgusting creature they no longer recognize, a creature controlled by Golbez, by Zemus... by Zeromus.
Zeromus is not a character. He is the concept of hatred. To be controlled by Zeromus is to be controlled by hate. This is the fulcrum around which the plot revolves.
Baron is controlled by Zeromus. It's controlled by xenophobic hatred of the other nations and desire for power and control.
The Red Wings are controlled by Zeromus. They're the inheritors of Baron's hatred, becoming a rogue military rather than laying down arms in the wake of Baron's liberation.
Kain is controlled by Zeromus. He's controlled by his jealousy and resentment over Rosa loving Cecil instead of him.
Even Zemus is controlled by Zeromus in a way, controlled by hatred of the new land the Lunarians have found. Zemus seeks to dominate and enslave these peoples he deems subhuman, because his is the hatred that drives colonialism.
So much of Final Fantasy IV is about this. It's why a major fixture of the setting is the Tower of Babel, an edifice from Christian mythology that Zeromus plans to use to destroy the peoples of Earth. Why the Tower of Babel? Why is that the superweapon?
"The Tower of Babel contains a giant robot that will blow up humanity" isn't exactly mythology-accurate. Why is this the superweapon?
Well, it's not because of what the Tower of Babel does, but what it represents. The Tower of Babel is the mythical origin of racial tension and division among peoples. The story of the Tower of Babel provides a religious explanation for why we're separated from each other, why we speak different languages, in a similar fashion to the way Zeus is the religious explanation for why lightning strikes in Greek mythology.
The Tower of Babel is Zeromus's superweapon because those divisions are the villain of Final Fantasy IV.
And the only way to defeat Babel's robot, to overcome the Tower of Babel, to vanquish Zeromus, is for the peoples of the world to overcome their differences and unite in cooperation and mutual respect. The only way to tear down the divisions imposed by the Tower of Babel story is for us all to stand together against hatred.
This is also the purpose behind Cecil's paladin trial. Because Cecil's hatred is hatred of himself for what he did to the Mysidians and to Mist. Cecil's self-hatred is still a form of hatred, still a force that Zeromus can control him with.
This is why Golbez ultimately proves incapable of defeating Zeromus at the eleventh hour. Because Golbez, like Cecil, carries hatred of himself, he can never vanquish the very hatred that he himself is feeding.
But Cecil's paladin trial prepares him for facing Zeromus by forcing him to lay down his sword and accept the darkest parts of himself. Only by letting go of his hatred can Cecil truly become a force for peace.
