The main boss, Rahu is an opponent you will fight alot through the
game. Every time you fight him he will have different weapons and
sometimes pods. Legs always remain the same. So, there is a Robo setup
that I found best and easiest to take him out. Every time I fought
Rahu I used this same setup:
Body: Ray 01 (Color doesn't Matter)
Pod: Dolphin Pod
Gun: Gatling Gun (I found this to be the most usefull gun available so
far.)
Bomb: Cresent (I never really used bombs when fighting Rahu, I did in
other matches though. I used cresent alot, but bombs can be aby you
choose really.)
Legs: Long Thrust

Strategy: Ok here we go. When you start off, try to morph from the
Robo Cube as fast as possible. If you get the first hit it always
makes a world of difference. Using the long thrusts you can easily
move from place to place. Quickly thrust to his current location and
unload a whole clip of Gattling Rounds on him. While he is trying to
reboot unload some more. Each time will do a good 100-125 damage or
so. If you feel you must use your bombs and pods then feel free too. I
never used them on Rahu.
(On Rahu III, the final boss, It's optional, but it helps to
substitute the Gatling Gun for the Dragon Gun. Just stand in one place
and whale on him while you team mates trach him down. But if the arrow
above his head turns red then move.)