After getting an "S" Rank on all fifty Tips & Tricks Battle Review mode missions.
Master Fighter mode
Get an "S" rank in all fifty missions in Battle Review mode. Master Fighter mode features an unlimited heat gauge.
Hidden Boss battle
Finish every one of the the side quests. Talk to the Boss that appears in front of the movie theater to begin another battle.
Intentionally fail the game three times. After three retries the game will ask if you want easy mode. REMEMBER: If you select "Yes" you cannot return to normal mode.
By finishing the game.