To get Brilliant Diamond Gemstone, all you need to do is get to a specific Adventure Rank's, then go to the Adventurer's Guild in Mondstadt or Liyue and claim your reward.
You will get two Brilliant Diamond Gemstone at the following Adventure Rank's:
- Adventure Rank 35
- Adventure Rank 38
- Adventure Rank 40
- Type: Jewels
These characters use Brilliant Diamond in Ascension.
These are the other Brilliant Diamond Jewels