As the quest describes, you need to get these two items from the large Shaula and Pollux key dungeons, i.e. the big story dungeons with the bosses at the end of them.

You will need to take Lotte along for her ability to spot invisible chests (see the two screenshots below).

Once there, if a PC user, you will have to position yourself slightly to the side and above of the ghosts and hold down both of the spell toggle buttons (i.e. the one which makes Lotte create a shield around her and the one where she twirls her wand around a bit - if she starts twitching like she's bugging out, you're probably doing it right).

And there you go; quest completed in 2 runs rather than +10-16 hours worth of grinding!




Note the map location in the upper right.



Ta-Dah!



And the last one.


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Notes:
- There is a small chance of the item not dropping from the chest. Worry not; this doesn't happen often, and there are actually two rooms with secret chests in each of these dungeons - both chests drop the item in question. I didn't bother putting both locations in due to frustration and laziness (sorry!)

- Users on the internet playing the PS4 version describe Lotte's skill as working by holding L1+R1, which would be one of the spell toggle buttons and the run button by default, hence why pc users have trouble figuring/finding out how Lotte's skill actually works - no idea why this was changed for the PC version, but after some frustrating face-rolling of the keyboard and internet sleuthing, I figured out the combination stated above. Hence the guide, so others can avoid having to look for this stuff.