The Cave Coin is going to be used as means of payment for upgrading your weapon rarity. Higher rarity weapons contain higher damage+stats and better effects. The basic cost per damage is calculated in a way that price will grow exponentially higher the more base damage and stats are contained within a single weapon. The penalty for upgrading weapon is paid in "Cave Coin".
Players may spend specific combinations of weapons of different rarities and cave coins, in order to craft (create and mint) any weapon of their choice.
Common weapons are used as an in-game currency for crafting weapons, as explained in the graph above.
The graph below shows the exact costs for crafting weapons per rarity.
Below are the value-cost analogies per weapon/item rarity type.