Defeat White Lion Musketeers around the Lost Mines area. Afterwards, speak to Guard Landau at the Dimita Oasis. Use your quest tracker to see your progress.
Guard Landau: I think I'm going to join the White Lions. NakanoAzusa: What? Why? Guard Landau: What do you mean, why? Why shouldn't I?! Look at Guard Landau: where I am and look at what they're making me wear: Guard Landau: chainmail and purple pants. HiiragiKagami: I think you look good! Guard Landau: You know I don't look good. HiiragiKagami: Let me guess, the captain asked you to make sure that HiiragiKagami: the White Lion situation is under control? Guard Landau: As far as I'm concerned, the only White Lion situation Guard Landau: there is is how long it's gonna take before my Guard Landau: application gets processed. The first thing I'm gonna do Guard Landau: is invade this oasis. HiiragiKagami: I think he's kidding. We should make sure that the HiiragiKagami: White Lions aren't causing too much trouble, though.
Reminder Dialog
Guard Landau: While you're out there, put in a good word for me.