See the Balterossan Soldier in Cafe Moondust. She will redirect you to Balterossa Castle to see the chief of staff.
Spoiler warning: This section may contain information that could spoil the story line or displays in depth quest or fight details.
It is "only" a boss battle. Before accepting the quest the quest giver will suggest using the formations Vanguard and Batwings. If you follow his advice, when the Mantroskylo uses Vulcanbreath, it will only damage 1/5 - 3/5 of your union members, on average, instead of all 5. You will face two Xi groups, four Omicrons and the Mantroskylo. Take out the enemies on the sides first, the ones on the bottom won't enter the fight until you engage them. The Mantroskylo has around 77,000 HP and gets an additional Vulcanbreath or Desperate Wail (if your morale is high enough) every two rounds.
Spoiler warning: This section may contain information that could spoil the story line or displays in depth quest or fight details.
Gossip
Athlum:
Pleasant Young Man: "Some monster army's appeared in the Great Sand Sea. They're so powerful that everyone in Balterossa is totally in despair... ...That's the story, anyway."
Bartender: "Only those who've known despair know the true meaning of hope... So, everyone should have the chance to taste despair at least once!"
Pleasant Young Man: "Yeah, well, this could be their first and last chance!"
Balterossa:
Bartender's Daughter: "A monster army has appeared in the Great Sand Sea and is threatening Balterossa. They're so powerful... it seems like we're in trouble. That's the latest news, Daddy."
Bartender: "Mmm, there is no reason to go to the Great Sand Sea... I will make certain I don't have any errands that would send you there, beloved daughter."
Celapaleis:
Gossipy Girl: "Some monster army's appeared in the Great Sand Sea. They're so powerful that everyone in Balterossa is totally in despair... That's the latest scoop, anyway!"
Bartendress: "Goodness! What could possibly be going on?"
Gossipy Girl: "Is the desert really gonna be okay?"
Elysion:
Mysterious Part-Timer: "A mob of ferocious monsters were spotted in the Great Sand Sea. They're apparently so powerful that Balterossa doesn't know what to do. Interesting, huh?"
Bartendress: "Drama! I should go have a looksie."
Mysterious Part-Timer: "...You're a loon."
Balterossan Soldier: "Balterossa is looking for men of action to assist in battle... I stress that this is an opportunity strictly for the experienced. If you have confidence in your abilities, come to Balterossa Castle and speak with the chief of staff. He will tell you what you need to know."
Chief of Staff: "A thousand years ago, there was a great kingdom in the desert. Its military was renowned around the world. And within that force was the queensguard - the Mantroskylo. Their prowess in battle is still sung in legend today. They were heroes who sealed countless wild monsters. A brotherhood who protected their queen like an iron wall. Skilled warriors who could win while outnumbered a thousand to one. However, they were eventually destroyed by their own strength. They turned into monsters, and turned upon the Imperator. The Imperator immediately struck back. After a fierce battle on both sides, the Imperator took the Tao Tie and sealed the Mantroskylo. Young traveler, this is no simple nursery-tale. After a thousand years, the Mantroskylo have returned. They assemble against Balterossa to take back the Tao Tie. This cannot be allowed, no matter the cost. Somehow, the force that was strong enough to even plague the Imperator must be defeated. Balterossa is calling all men of action to assist in its defense. Traveler, will you go to the Salamander's Belly and fight with us as well?"
Rush: "I can't fight a real army!"
Chief of Staff: "This is for your own good. War is not fought by lone men. Proper strategy is necessarry, and each has their role."
or:
Rush: "Sure, I'll help!"
Chief of Staff: "The Vanguard and Batwings formations would be best for this battle. However, both are lost arts. This will not be an easy fight."
Rush: "...Okay, time to give up!"
Chief of Staff: "This is for your own good. War is not fought by lone men. Proper strategy is necessarry, and each has their role."
or:
Rush: "Yeah - but I gotta try!"
Chief of Staff: "Then go, traveler!"
After we win...
Chief of Staff: "Ohh! Did you defeat the Mantroskylo?"
Rush: "Oh yeah!"
Chief of Staff: "I see, you struck without hesitation."
or:
Rush: "Oh no."
Chief of Staff: "You are surprisingly humble."
Chief of Staff: "Then, I give you this. Balterossa's crisis has passed. Still, why would the Mantroskylo betray the Imperator to begin with? Perhaps some day the truth will come to light. Until then, be well, young traveler."
