Demons: Demons can access the Demonic interactive weapon system once they receive their Demonic Weapon. This system not only allows the weapon to improve, but it also allows the user. This applies to all Demons, not only the main character.
Spirits: Spirits are granted blessings from mythological creatures and beasts that existed in their world before their extinction. These blessings enable them to transcend the very limits of reality.
Humans: Elemental Affinities.
Gods: Read to find out.