[The Chaos Entity]

When Gen Urobuchi was hired as the head writer for Kamen Rider Gaim, he said in an interview that the Riders and Henshin Items had already been designed, and that Takebe hired him specifically to make the fruit theme work.

So the toys come first, definitely - although Toei does have a say in what those toys look like. I recall Takebe thinking of a flat bird+samurai theme for Gaim, before Bandai came up with a fruit+general warrior theme.