Edge of Eternity

This does not unlock when you find the crystal fruits, but rather when you hand over to the quest NPC Grant.

Edit, following querry.

You get the Quest from Grant.
He is located near the Inn.


Here he is, on the bench.


He gives this quest.
You can hand over the quest for each 10 crystals you collect.
You will get a reward every time, with some added clue about the crystals.


Hope this helps.