Xenosaga Ep. 1 LLG Domo Carrier

The important part of this fight is the boss analyzes his event slot on his first turn, and uses it to give him a number of benefits. Boost Slot gives him the ability to activate tremor whenever boost is up (not good at all) and crit makes his tremor do way too much damage (also not good), the best slot for him to get is nothing, so this fight might wind up being more luck than anything. Ziggy is really the only option for a 3rd character besides Shion and chaos - he's the only one that's able to stand up to the boss' assault. Have your AWGS W-Act to deal the most damage possible and the boss will go down. Laser Rifle doesn't do a significant amount of damage so there's nothing to worry about there. You might want to use a veil on the boss as he can heal himself if given the chance.