The game allows you to level up your character to level 50. After your reach this, you have the choice to level up other characters or you can continue to upgrade your main character's equipment and explore all the game content. You can equip a ability stone to your character to get engraving nodes. To get some, there is Powder of Mystery, which you can get by dismantling ability stones.
If you're playing this game, then you have Ability stones in your inventory. You can refine them to try to get nodes on engravings to benefit your character. If the stone does not suit you, you can dismantle it to obtain Mystery Dust.
If you don't know what to do with your Mystery powder, you can sell it to a merchant in in-game capitals, such as Bern Castle, for ability stones to try and get better bonuses from engraving for your character.