Spirit Strikes
You are invincible when charging up for a spirit strike so you can use them defensively as well as offensively.

Beating the Spider Queen
Having trouble beating the queen down in the temple? On your mini-map you should notice that there are little indents in the room. Stand in front of one of these little indents and wait for the Queen to charge, move out of the way and she will be stunned. Then attack her from behind using combos like X,X,A+A+A+A or A,A,X+X+X+X. After the Queen starts shooting 3 purple blobs at you, change from combos to the tornado kick move. The long annoying battle will be a walk in the park.

Grave Stone Humor
Before facing Heigou, check out the gravestones in the Darkened Gardens. One is actually a reference to Zero Wing. It says, "All this grave belong to me." The rest of them are pretty funny too.

Defeating Central Processor Unit
It's all about the patterns. Use the photon pistol which should do about 250 damage for every shot. Shoot it once in the eye as it lumbers toward you then run away until you hear a clank sound. This is when the robot attacks and then returns to the middle to charges up. During his walk back to the centre get close, wait for his charge up and strafe sideways away from the beam. When he powers down walk backwards and get in another shot. Repeat. After awhile the robot will recharge via electro arms that come out of the wall, use your Nano-tech skill and shoot the arm. You should take it down quickly with the occasional 1000 points of damage. Start the dodging and weaving again. Eventually the robot will start malfunctioning and charge at you after you destroy 4 electro arms. It will now occasionally do a whirlwind attack. Just take your time and shoot the eye when you get a good line. If done right and you get the patterns down you should be able to do this without getting hit. Don't worry about the cylindrical robots that drop into the arena. If you keep moving you shouldn't get hit.