The only scripts I have are proprietary camera effects, so I can't share them. Once you find/buy/write a script for a blur effect, you basically just need to add that script to your main camera, make sure it's disabled, and then from your battle start event turn the script component on. There are fancy ones available that even allow you to animate the blur over time. Then when you fade to the battle scene (while the screen is faded at the end of your battle start event), turn the component back off so it returns to normal.
Have you tried importing the Standard Assets Effects package and playing around with what's in there (they'll be under Effects->Image Effects-> Scripts)? Here's Unity's documentation on it - you might be able to use a couple of those effects in tandem together and animate them over time to create an FF style transition.
Like for example you could use the Twirl effect and animate the Angle field over the length of your transition time to the battle scene, and maybe still a vignette or sepia thing on there too.
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Like for example you could use the Twirl effect and animate the Angle field over the length of your transition time to the battle scene, and maybe still a vignette or sepia thing on there too.