On demons’ signature spells and their personalities.
One thing I noticed watching/reading Frieren is that for most demons, save the few extras, or those of whom we haven’t seen enough to judge, their magic directly reflect their personality.
Qual is a direct, straightforward person, who says what he thinks, and his Zoltraak is a direct, straightforward spell.
Lugner is bloodthirsty and his magic is blood manipulation.
Draht’s wire is a powerful killing tool but has obvious flaws, which he overlooks, because these words also describe him as a whole.
Linie’s copycat magic can be read two ways. Either she is a hollow shell, with only a semblance of actual self, but given that she exhibits actual curiosity and pride in her skills, her magic is more likely to be meant an expression of her desire to learn.
Meaning of Aura’s magic is difficult to decipher, because in the manga/anime her dialogue comes as pretty generic villain talk. In her chapter of the first Prelude novel it still mostly is, but we get enough of said dialogue to see her angle. Aura believes that only the strong do can do what they want, while the weak have no freedom or agency in this world, Auserliese takes this to the logical endpoint, by stripping those weaker than her even of control over their own bodies. (This also means that “the Aura kept alive and conditioned with human values” setup loved by fanfic writers probably would simply make her conclude that she lost to humans because was not strong and ruthless enough, and that for optimal use of slaves they should be mentally broken, rather than merely beheaded.)
Jung wants to be closer to humans, so her magic allows her to masquerade as them. (In the anime it seems to be an illusion, though in her Prelude chapter her magic is turning into anyone she had eaten.)
Revolte is a case I’m not certain about. He’s an exemplary demon, probably the closest to Frieren’s description of a beast who uses speech only to deceive, yet his magic is imitating a legendary human weapon. In my opinion, Revolte is much more fascinated with humans that he admits. That is also indicated by the fact that he normally fights like a trained fencer, only falling into animalistic rage when near death.
Macht’s magic turns everything into indestructible gold, pretty, unchanging and completely useless to anyone but him. It’s inimical to all life. He’s does not like his own magic and prefers to fight without it, or keeping its use to creating weapons or shield for himself. The message, I believe, is obvious.
Solitar is knowledgeable, concealed and enigmatic, she had been hiding her face until coming to Weisse and loves to lie about herself, and we don’t even know what her magic is. Are flying swords really her signature spell? Why the spell is not named, then? Even spells of Hemmung and Solide were named, even though characters themselves weren’t (not until the factbook).
Grausam replaces reality with pretty illusions, because he is implied to hate his own actual form. One wonders what sort of eldritch abomination he must be, given that demons do not seem to discriminate each other by appearance.
And Rivale’s “magic” is needing no damn magic. He conjures weapons not to gain advantage in a fight, but to test himself against worthy opponents with weapons said opponents prefer.
All in all, pretty admirable attention to detail.