This trick requires the Sigma Blade and the Black Armor. It also works with only the Sigma Blade, however it is easier with the armor as Zero will be twice as strong. Choose Zero and any other character. At the beginning, equip the Sigma Blade and simply keep advancing trough the rooms. It should be much easier to get the top rank at all the rooms, as this weapon breaks enemies' barriers with a single hit, thus defeating certain enemies with just one hit. By doing this, you should have about a 60% chance (with Sigma Blade only) and up to 90% chance (with armor and Sigma Blade) of getting an "S" rank at all the rooms. Two of the three rare metals of this stage can be collected only if you get top rank on the rooms. Get top ranking on at least five rooms to get the rare metal for a life tank. Get top rank in all the rooms to get the metal for the metal generator. Note: Both will appear at the end of the stage where you collect the battle spools.