The way I see it…
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There’s magic energy in the air everywhere produced by that Chaos thing.
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When you charge your magic energy, you become some sort of antenna able to collect magic energy from the air.
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Magic circles are just a tool used by the majority of wizards to cast their magic until they “learn” how to cast magic without them (like curses or maybe the awakened form of your magic). I guess we can see magic weapons as another tool to cast magic.
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What you casted is just magic energy in whatever way you knew. If you only know fire magic, then you will only be able to cast your magic energy in the form of magic fire.
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Everyone has magic energy inside of them, it’s just that only wizard know how to use it.