These songs are unlocked in the Encore section of the Challenge series. Each song requires a certain amount of Rhythmia and has all 3 difficulties available.

Unlockable	How to unlock
Blinded By Light (FFXIII) (BMS)	15000 points.
Dancing Mad (FFVI) (BMS)	10000 points.
Searching for Friends (FFVI) (FMS)	20000 points.
Those Who Fight (FFVII) (BMS)	25000 points.