Successfully complete the game on the Devil Hunter difficulty to unlock the The Bloody Palace.

Successfully complete the game on the Dante Must Die difficulty to unlock the Super Dante costume.

Successfully complete the game on the Dante Must Die difficulty to unlock the Super Nero costume.

Successfully complete the game on the Devil Hunter difficulty to unlock the Son Of Sparda difficulty.

Successfully complete the game on the Son Of Sparda difficulty to unlock the Heaven Or Hell difficulty.

Successfully complete the game on the Son Of Sparda difficulty to unlock the Dante Must Die difficulty.

Successfully complete the game on the Dante Must Die difficulty to unlock the Hell Or Hell difficulty.

Successfully complete the indicated task to unlock the corresponding artwork:

Demon Invasion: Successfully complete the game on the Dante Must Die difficulty.
Light From The Demon Blade: Successfully complete the game on the Hell Or Hell difficulty.
The Cast: Successfully complete the game on the Devil Hunter difficulty.
The Demons and 12 publicity pictures: Successfully complete the game on the Son Of Sparda difficulty.
The Ladies Of Devil May Cry: Successfully complete the game on the Heaven Or Hell difficulty.
The Two Heroes and 29 character images: Successfully complete the game on the Human or Devil Hunter difficulty.

Successfully complete the game. Then during the credits mini-games, protect Kyrie for over 90 seconds to view the rest of the ending sequence featuring Dante, Trish, and Lady.

Use Grim Grip to reel yourself close to his head, and attack with your sword. Once the combos are done, use Grim Grip while still in the air. When his flames are gone, jump up to his head. Grab his head with the Devil Bringer, then once he lands from that, use Devil Bringer again to throw and punch him. Then, run a short distance away because he will release an explosion around him. Make sure to pick up Green Orbs from the destroyed buildings, and roll to avoid his flame geysers and sword attack. Continue attacking this way, and use your Charge Shot to defeat him in under a minute.