Completion bonuses:
Beat the game to unlock the “Movie Viewer” option and a mini-game featuring Tachikoma.
Weapon bonuses:
To get a dual wieldable version of a handgun, play through a level with only that handgun. You will be able to equip both of the handguns in one weapon slot.
Collect a weapon that is not in your inventory during the game, then have it equipped when completing the level. When the next level begins, it will be a part of your available inventory.
Beat all Single Player mode levels with a character to unlock his or her custom weapon. After unlocking it, the weapon can be used by any character.
Special Tachikoma:
While playing through a level, look for a yellow/orange box-shaped robot carrying a red and white fan. If you kill him, you will be rewarded with a special Tachikoma part when you complete the level. If it was the correct robot, you will see a “Tachikoma Part Obtained” message appear once it has been killed.