You must beat Story Mode with every character. After this is done you can go back and play the stories again. After beating them, you will get to read part of Gerald's Journal!

Effect - Code

Gerald's Journal entry #1 - Beat Sonic's story again
Gerald's Journal entry #2 - Beat Tail's story again
Gerald's Journal entry #3 - Beat Rouge's story again
Gerald's Journal entry #4 - Beat Knuckle's story again
Gerald's Journal entry #5 - Beat Amy's story again
Gerald's Journal entry #6 - Beat Cream's story again
Gerald's Journal entry #7 - Beat Shadow's story again
Gerald's Journal entry #8 - Beat Emerl's story again