My number 1 pick is Kefka. The sick joy he takes in killing and his utter disregard for life would definitely earn the girls' hate. Not even Pinkie Pie would laugh at his antics.

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I can't argue. Besides that maybe Sephiroth due to the fact but they would likely be very close to Aerith. The main villains of 13 and 15 are also likely candidates. Final Fantasy IV is complicated due to the nature of Golbez and the bigger bad of said plot.

I've finished Chapter 1 of Final Fantasy Tactics earlier, and I feel like I should add Algus/Argath to the list, given what he did to Delita's sister.

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Not sure if spinoffs have been mentioned yet, but I more than welcome them.