The 3 ways to heal are to use the starpower skill, which tends to be quite weak during combat, but can be useful at low health or to stall, the "Holy slashes", that deal damage and always heals the same set amount, and the "Life ender", which aborbs enemies HP. During the final boss, you also get a regen effect although this is something I didn't display properly. You can use starpower outside of combat.