This area can be entered once all six base battles have been cleared.
The battle works in a similar way to the fights at the bases. At the beginning you will be facing four units of Stormtrooper Aces and two of Special Aces. As their name implies, the Aces are much tougher than their regular equivalents - watch out for the Special Aces in particular as their use of Explosives can come as an unpleasant surprise.
Three more unions of Stormtrooper Aces appear next, followed by two Special Aces the next turn. When you have defeated all of these, the boss makes his entrance. Note that unlike the base battles, this is still part of the same fight so you will not have your HP, AP or ailments restored.
The Ala Melvilana Synthesis is a huge boss, towering over even the Cyclops, and is accompanied at first by two unions of Support Aces. The next turn, two Stormtrooper Aces will appear on your left flank and two Magus Aces on your right. As with all boss battles it is advisable to mop up these weaker unions before concentrating on the main opponent.