At the 'Pause' menu enter the following codes to enable the corresponding effect.
Regain ALL Health:
Holding R, press Down, Down, Up, Down, Left, Right, Square.
Regain ALL Stamina:
Holding L, press Right, Up, Down, Left, Up, Down, Square.
Boss Mode Modifier Codes
Boss mode must first be unlocked for the following codes to work. The following modifier's are enabled by holding down the corresponding button while selecting the Boss Rush option.
HP / WP Restore After Each Battle:
Press Y Button
Infinite Weapon Points:
Press X Button
Nightmare Mode Difficulty:
Press L Button
Ultimate Zangetsu (Full-Powered):
Press R Button
Unlock Boss Rush Mode
Once you have unlocked Nightmare and Ultimate mode you will automatically gain access to a feature called 'Boss Rush' where you have control of ALL 4 party members and a selection of their subweapons. You will only be able to equip one subweapon per character per fight and Zaangetsu will not have any of his powers from the Bad Ending route.
Unlock Ultimate Mode
Ultimate mode becomes unlocked when you have beaten Normal mode but instead of recruiting your companions you killed them. When you do this Zangetsu will gain their souls and a special ability from each of them. Ultimate mode lets you replay the game with Zangetsu's abilities and the opportunity to recruit your companions.
Unlock Nightmare Mode
Nightmare mode will become unlocked once you have beaten the game on Normal mode and it will continue the story and give you immediate access to ALL the characters except Zangetsu.