It was easy for Rae to make physical constructs because he knew that there were atoms and many other small molecules that made up the bigger things.
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He had decided to create the smallest part of ki he could, and then decided to make physical constructs as a foundation with that logic.
This helped him make thin shields which he constructed from puzzle like small constructs, like a Lego.
The constructs he made in the beginning were very small but hard, and later on he began to manifest numerous small constructs and combined then to make a big one, causing his constructs to become stronger and durable.
"But in the spells, we have to make the figures and diagrams with ki and make it interact with the body. It could a physical construct or a flow of ki in that shape."
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