There are four weapons that are obtained from the god orbs, one for each of your characters:
The first you have to get is Atsuma's. Get this when you visit the sage. Afterward, there are three more you must find scattered throughout the game. One sage is right outside the sages' area you just go down the stair case and look around the entire tower; there will be a golem there. When you kill him you will get its core and a god orb.
Another one is in the desert outside the Junk City in one of the ruins, but the doors to it are locked. On the middle right side of the area, between the 2 ruined buildings, is a sink hole. Go to it and you will fall through there is another golem there who will give you a god orb after you defeat it.
Then there is the area where the Yokahama bridge was blown up. Go down to the river like you did when you swam across the first time, only this time don't go across. Instead, go down to the part of the river where you see pieces of a statue blown off. There will be a sandy part on the shore where you can get out. Walk around that area until you find the last golem in a kinda corner and you can get the last god orb from it
God orbs make the Iris wepons, which are the second strongest in the game (the strongest are the crystal weapons, which are found in the holy beast area outside of junk city; you can also find omega golem, one of the strongest golems obtainable).