Goodness, the Extra Boss' last spellcard and the hidden Extra Boss' first spellcard are both insane! I've no idea on how to capture them, or at least get through without wasting 2ish lives!
EDIT:
Also regarding the passives, Shitodo's Passive is that she regenerates that flashbomb gauge passively. Saragimaru's passive is, as far as I can tell, having a flash bomb that injures enemies. Also, whenever they fill a spirit gauge layer their flash bomb meter increases VERY quickly. To the point you can drop two or even three flash bombs one after the other and still end it with a full gauge.
It seems that Sukune and Yaorochi's spirit gauge layer passive is having both them shooting at once. No clue about Yabusame's team's, but I think it has to do with autobombing.
Anyone knows Tsubakura's secret passive?
The passive abilities are active when the character in question is in the backseat (at the bottom of the screen). During Spirit Mode, getting hit will automatically counterbomb for you.
Spirit Mode Ability: Auto collect items and grant the Power to both characters
Yabusame: Automatically moves to collect items
Tsubakura: Grants the primary character the ability to collect spirit items
The "secret" the manual refers to is probably being able to hit the stage 6 boss through one of the spellcards... I think
Spirit Mode Ability: Both characters attack at the same time
Sukune: Items move towards Sukune
Yaorochi: Deals damage to all enemies and clears all bullets on the screen when the Flash Bomb gauge reaches MAX
Spirit Mode Ability: Regenerate your Flash Bomb gauge rapidly
Kuroji: Increases the amount of Flash Bomb generated by grazing
Saragimaru: Passively regenerates your Flash Bomb gauge