Submerged City

Once you're ready, go to the Elsa's bridge, talk to Capt. Matthews and head for Old Miltia. Outside, save your game. Continue west to the next screen. Keep going onwards to the next area once more. Here, head left at the split, shoot the wall to knock it down. Pick up the treasure chest with a Quick Charge at the end.

Go back down to the main path, and shoot the obstacles to get a G Weak Guard. Go east to the next area. At the split, take the upper path heading right, exit your E.S. at the end. Blast the rocks to find Segment Address #18. Get Secret Key 16 inside. Make your way back to the fork, and this time take the lower path. Blast the objects here for a Nano Repair A and a Nano Repair Z. Continue east to the next screen.

In this area, head north a bit to fight 0-88 Delphinus. Be sure to steal G-Power Charge, since it'll come in handy later. Also, casting Aura Sword on your E.S. will make this battle somewhat shorter. Continue forward up the ramp, then south to save. From here, go east, then south onto the slab of wreckage. Blast the objects along the way for a Nano Repair A.

Go up and shoot the piece of concrete slab, to make it fall into the water. Head back, then go north across the water. Continue west to move on. Go west some more and follow the path to the end, picking up a Nano Repair Z along the way. At the end of the path, you'll encounter a fork. Go south, fight another 0-88 Delphinus. Pick up the treasure chest containing Decoder 9 behind it.

Return to the fork and head north. From there, go east, shoot some more obstacles to get Nano Sphere (x2). Head west to the next area. Now go north and defeat the last 0-88 Delphinus. Destroy the obstacles to get a G Poison Guard. Save your game and move on. In the next area, go forward to trigger a cut-scene, then a boss fight.

Naglfar Cannons

This is another easy fight. The key here is to attack the cannons during the designated event slot, where its defense shield is diverted to other areas. Hit it twice at this point to destroy its defense totally. It also helps to equip G Weak Guard or G Power Charge, for protection against L Weak (Physical Defense Down)

Have Ziggy pilot Asher with Jr. to utilize the power of Corona Buster against this boss. Tornado Fist (KOS-MOS, Shion combo) is also very effective. Only use special attacks when the cannons' defense shields are out. You should win real quick. Watch out for for Fire Cannons 2 though, since it's pretty powerful. The auxillary fuel will give the cannons additional 6000 HP, but that shouldn't be much of a problem either.

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After that battle, proceed right to the next screen. You can't get into the tower aboard your E.S., so you'll have to look for another route. Blast the obstacles for a Nano Repair A. Continue forward a little further, destroy the boxes to reveal a treasure chest containing a G ST Double. Shoot the yellow object a little bit to the left, exit your E.S. and climb down the ladder.