Real Robot Regiment - Platform: Playstation 2

Full member mode
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Hold L1 + R2 + L3, then press Start at the title screen. 
A sound will confirm correct code entry. 
Alternately, successfully complete the game in story mode.

Gundam
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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
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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.

Hard difficulty setting
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Hold R1 + L2 + R3, then press Start at the title screen. 
A sound will confirm correct code entry. 
Alternately, successfully complete the game in full member mode.