This is regarding the tiger girl that initially spawns in the southernmost part of the forest in the southeastern part of the continent; if you manage to get to the bottom part of her lair before you progress to postgame, you are rewarded with two chests, the left one contains a 精力剤EX (boosts number of attacks by +1 during battle, consumable) and the right one contains 1x gold bars. I found you can actually get this extremely early by using a speed potion, which can be stolen from the thief girl you practice with in the tutorial. For anyone who doesn't know, you can practice with her downstairs in the Inn. I'm assuming you can also get past the tiger girl by simply beating her before the post-game, or by using the stealth skill. Admittedly, it took me at least 10~20 reloads to speed past her, grab the chests, and run back out of the lair.
Sorry if this has been mentioned before. I'd check, but the search function in ULMF doesn't work at the moment.