New Game +:
Beat the game to unlock New Game+ mode. Additionally, in Chapter 2, you can enter ReanBell's (Leanne's) bedroom and press [Action] at her wardrobe to activate a secret button. It will allow Reanbell to remain in her current costume instead of changing into the pig T-shirt in the cinematic.
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 X to advance to the next line of dialogue and unlock the corresponding costume:
COSTUME - HOW TO UNLOCK
Politan Suit - Press R3(3), Right, Left, Y, X, LT, RT, LB. Note - Earn the Reindeer Suit in Neverland first.
Gemaga shirt - Press RT, LT, LB, RB, Y(3), X(2), Up.
Platform Logo shirt - Press RT, RB, R3, L3, LB, LT, Right, Left, X, Y.
8-bit Girl shirt - Press Up(2), Down(2), Left, Right, Left, Right, Y, X.
Hirakou shirt - Press X, Y, LB(2), RB(2), L3(2), Up, Down.
Club Famitsu shirt - Press Y(2), Up(2), X(2), Left(2), LB, RB.
First Contact - A trophy for defeating your first enemy.
Maiden Mission - A trophy for clearing your first mission.
Bonus Hitter - A trophy for landing your first Bonus Hit on an airborne foe.
Tri-Attacker - A trophy for using your first Tri-Attack.
Hundred Plus Club - A trophy for raising a character's level to 100.
Bullet Barrage - A trophy for landing a combo of over 500 hits.
Resonance Miser - A trophy for storing over Resonance Points.
Hero Actor - A trophy for attacking over 1,000 times during Hero Actions.
Spite Monger - A trophy for landing over 100 Bonus Hits.
Extreme Spiker - A trophy for performing over 100 Smackdown attacks.
Professional Hunter - A trophy for defeating over 3,000 enemies.
Material Collector - A trophy for destroying over 3,000 enemy body parts.
Thousand Pitcher - A trophy for throwing over 1,000 attack items.
The Iron Fist - A trophy for defeating over 30 enemies with no weapon equipped.
Big Shot - A trophy for dealing over 2,000 damage in a single attack.
Material Creator - A trophy for having fused and scapped items over 200 times.
Shopaholic - A trophy for spending over 500,000 rubies on clothing and accessories.
Customaestro - A trophy for connecting over 10 custom parts to a firearm.
Basels' Repairman - A trophy for making over half of Basel's hexes accessible again.
Four-Terminal Chain - A trophy for connecting four distinct terminals.
Platinum Trophy - Earn all Bronze, Silver, and Gold trophies.