Pause the game, then hold R1 and press Square(3), Circle. Release R1, then hold L1 and press Triangle(2). Release L1, then hold and press R1, Square(2).
Pause the game, then hold L1 + R1 and press Circle, Square, Circle, Triangle(2), Square, Circle, Square. Repeat this code three, four, or five times to get the Soul Sword.
Pause the game, then hold R1 and press Triangle(4). Release R1, then hold L1 and press Triangle(2). Hold L1 + R1, then press Triangle, Circle, Triangle.
Get all the grades, then you should get the "Master" grade. The Battle Arena will now be open in Robot Beach.
To get stronger swords, you have to kill enemies. Notice that when you complete a mission (at the blue screen with Ninja floating), there is a sword at the bottom of the screen called "Ranx Bank". The sword has numbers that increase with the more "Ranx" that you kill. Also, the more "Ranx" you kill, the sword gets covered in Ranx blood. When the sword is full of Ranx blood, at the "Mission Complete" screen, Ninja will be holding his old sword. He will drop the old sword and a new one will fall into his hands.
Whenever you kill an enemy in a rapid succession, the number to the right of the health bar increases by one up to 10. This represents what points you receive for killing an enemy, multiplied by the number displayed. This is useful in certain missions where a high score is required to earn the grade.
If you are low on health, try to find some weeds and chop them down. Notice that your Rage Ability switch will gradually increase. Keep chopping down weeds and you will soon be able to use your "Ninja Revive" to heal yourself. If you are low on health, use the Ninja Fury. You will recover some health.
Where there are grass, flowers, mushrooms, other foliage, objects other than crates and barrels, and certain decorative objects, you can cut them down to earn a few extra points towards your main score. This is useful in the certain levels that require a high score to earn the grade.
In the first part (where there is lava for a field), keep a steady pace while jumping around on the stones. Hold Forward and the direction that you want to jump and collect the shuriken. Throw it at him without locking on. After throwing the full amount of eight shuriken three or four times, he will fall down into the lava. Then, he will jump up and absorb the lava. You will now have to sword fight him. The Soul Sword and Revive Rage are recommended for this. If you run at him and slash repeatedly, you are going to get hammered. The best times to attack him are when he just finishes a quick slash and when he is just about to do the non-shock wave ground pound. Hit him at those times and use Berserks and Insane Rages every time you do not need to revive.
Attack his belt. After you attack it twice, he will slam his fist. You can now attack it two more times before he slams you away.
To damage Psyamon, you will have to use your Power Bolt attack. Just shooting him with your miniguns will not effect him. Psyamon will shoot a red ball of energy at you. If it hits you, it will do a significant amount of damage. To avoid it, shoot at it with your miniguns to blow it up. He will then open his mouth and release Wraith Ranx (ghost-type Ranxs) at you. Shoot at them as fast as you can, as he will release a lot of them. When you kill one of them, your Power Bolt gauge (the gauge at the bottom right corner of the screen) will rise. When the gauge is full, you will be able to shoot your Power Bolts at Psyamon. As the battle continues, Psyamon will get much tougher. For example, after you damage him once, he will also shoot a blue ball of energy at you. If it hits you, your robot suit will malfunction, causing your movement to fail. To avoid it, shoot at it. He will also release more Wraith Ranx at you. Repeat the process five times to kill Psyamon.