Fifth story:
To unlock the Fifth story, beat the first four stories with at least a “Silver” rank.
Chaos difficulty:
To unlock Chaos difficulty, beat all stories with an “S” rank.
Additional item slots:
Enter the Buy/Ability menu. Purchase all the upgrades for the stat in the level you are in to unlock another item slot.
SLOT – LEVEL
Third slot – Musou: Acendancy
Fourth slot – Musou: Swordsman
Fifth slot – Musou: Stealth