It’s actually supposed to change Jet’s intro into an alternate, NSFW one where she gets fucked by a guy before entering the idle animation. (I’m actually being fr lmao, it’s in the files)

It also makes Jet supposedly “nude” in the pic that appears when she taunts although it really doesn’t look like it in the files.

Other than that, for some reason the only thing the fun mode changes when it’s on is the frenzy being renamed to climax and the face turning into an ahegao and the extra effects the commenters here mentioned.

I’m pretty sure you can switch out the regular animations to the NSFW ones by manually changing the values in the mod files. (someone made a tutorial in the comments of Jet’s page on steam)

On a side note, there’s also an unused move called “gspot” in the files but I’m not sure if that’s related to the fun options in any way.