Unlock Full Member Mode  -  First clear Story Mode once. After that, press and hold L1, R2 and L3 at the title screen, then press Start. You should hear a muted shout.

Unlock Hard Mode  -  First, clear Full Member mode once. After that, press and hold R1, L2 and R3, then press Start. You should hear the sound of a Megasaurous cry.

Gundam:-  Hold L1 + L2 + L3, then press Start at the title screen. A sound will confirm correct code entry. Alternately, successfully complete the game in story mode.

Hyaku Shiki:-  Hold R1 + R2 + R3, then press Start at the title screen. A sound will confirm correct code entry. Alternately, successfully complete the game in full member mode.