Board Thread:The Last Sovereign Discussion/@comment-87.58.238.209-20200222173850/@comment-39403387-20200229201148

You recieve the Crystal by providing substantial help to the Goddess of Magic cult during the Gawnfall Council. Talk to them in their base after the council is over, and they should give it to you.

And if you didn't provide enough help, I'm sure you'll get more opportunities to get a Crystal in the future.