Re: [RJ120635] [Eclipse works] Ariadne
Quest 30 is given by the pixie in the Witch's shop in Death Desert. If you have been there before it should be the leftmost teleportation circle after using the Warp Stone (Fragment). If not, starting from the Sun Temple go west and look for an oasis near the sea.
As for how to unlock the quest: you need to 'level up' the shop by buying enough stuff. In other words, spend enough gold. Keep in mind that 'leveling' is not immediate and you have to sleep a night and talk to the pixie again in order to notice anything. The exact amount of gold in order to do this is unknown to me. It's at least 61 gold and at most 11000 gold.
I'd say the quickest way if you've already done everything else is to save right in front of the pixie, spend some gold, warp to an inn, warp back and check if something has changed in the dialog. If not, reload your save file and up the amount of gold. If yes, repeat. If you want to play the game naturally, just stop by the shop occasionally during your adventure and buy some stuff. Daily, if you can be bothered. At some point it's going to give you quest 30.
Also take a look at etigoya's guide:
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It's a pretty fun quest to do, especially if you've played Magica before, and the rewards are pretty nice as well. Make sure to check back at the shop after finishing the quest to get the Wizards's memo.