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You can get this ending if you defeat the Time Devourer after Dario is fought but before the Terra Tower rises.  The ending scene occurs in the Viper Manor; the kids of the orphanage stands before the General Viper, who instructs them to work hard and play hard. An Acacia Dragoon talks to Dario and suggests a Dragoon youth camp; the two laugh as they formulate a plan to provide funding. Lynx, Harle, and Kid appears as well, arriving in Termina. They enter the Dragon's Tail bar, which is now staffed by the Devas and Lucia. They ordered drinks. This is available when you defeat the Time Devourer while the Terra Tower is still in the sky.  In the ending, the Sage of Marbule, the Dwarf Chieftain, and the Dragon God meet at the top of Sky Dragon Isle. The Dragon God instructs them to begin wiping out humanity in El Nido with their respective forces. The Dwarf is eager while the Sage questions this course of action. Nonetheless, it is carried out and demi-humans now populate the islands. Harle walks around Arni, overhearing conversations concerning how filthy the humans were, and then she picks flowers and lays them on a grave at Cape Howl, Serge's gave to be exact.

Summary:
Get the Career Change ending. Get the Return of the Downtrodden ending.