Defeat White Lion Hopefuls and White Lion Judges near the Entrance to Lost Mines West. Then talk to Agatha Brooks at the Resistance Base. Use your quest tracker to see your progress.
Agatha Brooks: Now the White Lions in the mine area are Agatha Brooks: almost gone, except for the ones in the Lost Mines. Agatha Brooks: I'll make sure to report your accomplishment to the Agatha Brooks: Congress. NakanoAzusa: Thank you. Agatha Brooks: There's still a long road ahead, though. There's one Agatha Brooks: strong enemy left. HiiragiKagami: Could that be...? Agatha Brooks: I don't know what you're thinking about. But the Agatha Brooks: next target is just more White Lions. These are Agatha Brooks: extremely strong. Their strength is equivalent to Agatha Brooks: boss level monsters. NakanoAzusa: Oh, I really don't want to fight them. Agatha Brooks: If you don't want to, you don't have to. I'll just Agatha Brooks: report to my superior that- NakanoAzusa: No, no. I'm glad I can do it!