The Record Keeper sprites were either taken from All The Bravest, another mobile game, or original to the game. A lot of the alternate sprites are based on Amano artwork.
https://www.spriters-resource.com/mobile/finalfantasyrecordkeeper/
They're generally based on the FF6 style, but not exactly the same.
Edit: Oh, I see what you mean.
He/Them
"Am I a butterfly dreaming I'm a man... Or a bowling ball dreaming I'm a plate of sashimi? Never assume that what you see and feel is real!"