Upon using the Synthesis materials that you may acquire from selling Demonite, you are able to acquire the higher rarity of Demonite.
The parameter for the higher rarity of Demonite will ramdomly determine after the exchange.
※Where is the Demonite Synthesizer: Home > Map > Alter-World > Bureau of Divination > Armaments > Third Panel > [Synthesizer] at the lower left side of the screen.