During or after Chapter 7, select Leanne and look at the wardrobe in her room. Enter one of the following codes when she says "Hmm, I think that outfit is in here...", then press A to advance to the next line of dialogue and unlock the corresponding costume:
COSTUME - CHEAT CODE Politan Suit - Click RIGHT Analog-stick(3), press RIGHT, LEFT, Y, X, LT, RT, LB. Note:Earn the Reindeer Suit in Neverland first. Gemaga - Press RT, LT, LB, RB, Y(3), X(2), UP. Platform Logo - Press LEFT, UP, RIGHT, DOWN, RB(2), LB(2), click LEFT Analog-stick. 8-bit Girl - Press DOWN(2), UP(2), LEFT, RIGHT, LEFT, RIGHT, Y, X. Hirakou - Press X, Y, LB(2), RB(2), click LEFT Analog-stick, press UP, DOWN. Club Famitsu - Press Y(2), UP(2), X(2), LEFT(2), LB, RB.