This heist aims to take down the massive Exploiter Orb that guards the Temple of Profit, and is acquired from Eudico in Fortuna's backroom.
Prepare to fight Exploiter by condensing diluted Thermia using the machine in Deck 12.
(upon starting the heist) Eudico: "Head to Deck 12 and load the Thermia into the Condenser. Then we start planning an attack on Exploiter."
The Tenno must leave the backroom and enter the Orb Vallis to continue.
Eudico: "Nef's using the Exploiter Orb to mine those fractures. One breach, and Fortuna's concourse floods with Thermia. We tried taking Exploiter down, back in the day. We… we have to try again, but this time we have to succeed. We don't, it'll be Deck 12 all over again… and I can't have that. Zuud and her sisters built a thermic condenser. Load it with Thermia and we can start prepping for a fight."
From this point, the fight against the Exploiter Orb is carried out the exact same way as it was during Operation: Buried Debts.