This will explain how to unlock the game's hidden Chapters.
Unlockable - How to Unlock
Akasaka Storyline - Finish at least Three Keiichi Chapters.
Miotsukushi-hen - Finish both Taraimawashi-hen and Tsukiotoshi-hen.
Shion Storyline - Finish Watanagashi-hen with Keiichi.
Taraimawashi-hen - Finish Keiichi's, Akasaka's, and Shion's Storyline.
Tsukiotoshi-hen - Finish Keiichi's, Akasaka's, and Shion's Storyline.