[Kleeyook]

Originally Posted by whsie

This was briefly explained by the mother to Miyuki.

Spoiler for explanation:

The mother explains that a "true magician" is one that can manipulate the information layer in objects. They can change a object from A to B. Tatsuya, no matter how little the task, was no able to accomplish this. His two natural abilities- disintegration and restoration- merely destroy, restore, or rewrite an object. In essence, he's isn't "creating anything new". He merely works with what already exists. In that sense, Tatsuya is not a true "magician". And if you're not a magician in the Yotsuba family, which is one of the Ten Numbered Families, you can't be treated as a Yotsuba.

When Miyuki heard this, she was stunned. She thought to herself, if her brother's ability is not "magic", then what does that make their abilities? What's more, if not "magic", then what do you consider Tatsuya's abilities? A "miracle"?

Thanks whsie!

The reason is quite something though. Tatsuya kind of remind me of The God's Right Seat from TAMNI where they have the power of god and is extremely powerful yet because of that they can't use normal magic. Or how Espers can't use magic since they'll suffer rejection and receive fatal injury from within.