Examine the dresser on the corner of Parin's room to change costume.

Unlock Armor:
Give 30 Gold Medal to Hyperbolic on Beginner mode

Unlock Princess Dress:
Give 30 Gold Medals to Hyperbolic on Normal mode

Unlock Samurai Outfit:
Give 30 Gold Medals to Hyperbolic on Crazy mode

Unlock Pajamas:
On Normal mode get the Good ending.

Unlock Monkey Suit:
On Beginner mode get the Good ending.

Unlock Chinese Dress:
On Hard mode get the Good ending.

Unlock School Uniform:
On Happy mode get Good ending.

Unlock Leopard Suit:
On Crazy mode get the Good ending.

Unlock Kimono:
Set PSP date to January 1-7

Unlock Santa Outfit:
Set PSP date to December 25-31

Unlock Maid Outfit:
Buy from vending machine at Spinach Caverns - Shadow Grotto

Unlock Vampire Outfit:
Give 30 Gold Medal to Hyperbolic on Hard mode

Witch Outfit:
Give 30 Gold Medal to Hyperbolic on Happy mode

Unlock Workout Gear:
Clear Boss Rush on Beginner/Normal difficulty

Unlock Work Uniform:
Clear Boss Rush on Hard difficulty

Unlock Nurse Outfit:
Clear Boss Rush on Happy difficulty

Unlock Swimsuit:
Clear Boss Rush on Crazy difficulty