You must view specific events and reach heart level milestones for a girl before a certain chapter to unlock her route. Kanami: 3 hearts by Chapter 8, 4 hearts by Chapter 12. Shizuka: 1 heart by Chapter 6, 3 hearts by Chapter 12. Tilde: 3 hearts by Chapter 11, 4 hearts by Chapter 13. Sen: 1 heart by Chapter 9, 4 hearts by Chapter 14.
Unlike MP or stamina, Rance IX uses a shared party-wide AP pool. Every skill a character uses costs AP. You start with a limited max AP (usually 3-5) and regenerate only a portion each turn. rance ix guide