Aside from the main weapons that can be unlocked by playing Red Steel 2, there are weapons that can be unlocked by entering a series on number under the Pre-Order codes. The following codes are confirmed to work on the US and PAL copy of Red Steel 2. Only two weapons can be unlocked at a time but those can be changed anytime.
Here are the step by step process in unlocking the weapons:
From the Main Menu, point the cross-hair to EXTRAS.
Point to Pre-Order Codes
You will now enter a series of numbers:
SWORDS / KATANAS
360378 (Kuro No Ken)
360152 (Nihonto Hana)
GUNS
3582880 (Barracuda)
370402 (Tataro)
