After completing the game on any difficulty and load the cleared game, you get the following effects other than your stats and moves re-set:
1. New costumes at the shop. (A guy at the left side will have them)
2. The technique section has all moves to buy and some new ones that are really expensive but worth buying as they are powerful.
3. You can buy nearly all Roulette moves in the shop including some new ones e.g. full recovery of health, charge up some of the tension gauge, etc.
4. Money value doubles e.g. collecting a 200 gold coin will be doubled in value (You get 400 instead, max you can earn now is 4000 rather than 2000), so you can buy good items and moves early.
5. You can buy all health, combo, tension and roulette upgrades from the very start without waiting until the next chapter.
Chihuahua Race: Clear Stage 2, then talk to the male NPC in the shop to play it.
Fighting Ring challenges: Clear Stage 1.
Fighting Ring Battle 41-50: Beat the game once.
Fighting Ring Battle 51: Clear Fighting Ring Battle 41-50.
Hard Mode: Beat the game on Normal Mode once
Costumes: All the 4 costumes,Carnival Devil Hand Karate and Olivia's Bunny Girl, are unlocked by beating the game once, in the second round there will be an extra NPC in the shop, who will change your costumes.