Blue Diamonds are a special currency that can be obtained through donations. You receive one Blue Diamond for every $10 USD or equivalent currency donated. Once the donation is successfully processed, the Blue Diamond will be sent to your account in your in-game purse. After obtaining your Blue Diamonds, you can spend them at the NPC Poporing, located southeast of the main city temple.
If you are far from the temple, you can also open the Blue Diamond shop by using them, which will have the same effect as opening the shop with Poporing.
These Blue Diamonds are used to purchase a variety of special cosmetics, such as wings and auras. The shop also has various items, such as bonus scrolls and dungeon charges. Please note that the cost varies from item to item.