You have to face Gargoyle in the Gnosis Cathedral Ship. The Gargoyle actually 
Commander Cherenkov. You need to have Shion, chaos, and KOS-MOS fight. Make sure 
that you have the upgraded frame and generator parts for Shion's and chaos's A.G.W.S. 
units. Equip both A.G.W.S. units with a sword since the Gargoyle and other Gnosis 
aren't good against close range attacks. Make sure everyone is at least level 18 or 
higher. When the battle starts, get into the A.G.W.S. units, and only attack the 
Gnosis on the right until it is dead. Why the Gnosis on the right? Because it can 
heal the Gargoyle 600 hp every turn. Then have KOS-MOS use med-kits on herself 
until she is fully healed. Finally attack the Gargoyle.