Completion Bonuses:
Save the game when you have successfully completed it then reload the
cleared game file. The Game Record, Mania and Sound Test options will now be unlocked at the Title screen and if you go to the Grade shop you will be able to access new items.

Fight against Aviation:
Once you have all 9 Darkness Weapons go to the Darkness Temple to fight
Aviation.

Falcon Crest:
Use the secret tech by pressing X+A +B which is called the Falcon crest when Lloyd is low on health (red) and he has the Material Blade equipped.