The following cameo characters can be unlocked by completing the corresponding task.
Lose against Raspberyl in Stage 1-5.
Fuka and Desco:
Complete 'Death Inst., Majin Academy Part 2', then unlock the Postgame.
Gig and Revya:
Complete 'Evil Academy Culture Fair', then unlock the Postgame.
In Survival mode, get 7 Level Spheres and wish for the Mascot character.
Play the main story again.
Rutile and Stella Grossular:
Complete 'Death Inst., Majin Academy Part 2'.
Added by: Sanzano Jan 14th 2013, ID#76