Finish the game once and complete the following songs in order to unlock extra characters during a 'New Game Plus' Play through.

Character	How to Unlock
Adult Mikuru Asahina	Play Chapter 5 in Story Mode
Asakura Ryouko	Play Bouken Desho Desho (Chapter 2) in Story Mode
Kimidori Emiri	Play Greed's Accident (Chapter 6) in Story Mode