It's called Imaginary Numbers, which...is a little complicated if you aren't familiar with system of magic my world uses, but I'll try my best to make it clear.

I can manipulate matter made out of ether in place of manipulating the other four elements--fire, water, wind, and earth. Ether is a form of artificial magic energy, and it can't attain a real physical form. But spirit beings can use ether to materialize in the physical world, it's what their bodies are made out of. So, in short, I can harm spirits and other immaterial beings. It's mostly useless against anything not made of ether...most living people.

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I-I can also perform regular magic, but I don't have any proper training, so I can't fight with it.