Nathan had indeed combined several concepts. Originally, he was inspired by the concepts in the novels.
There was a protagonist who could do alchemy outside the pot by using the flame as his pot. There was another protagonist controlling flying knives with his energy. Last but not least, he had seen another support character that had flying turrets around her.
He was inspired by these concepts and turned them into a single system. To achieve it, Nathan first had to learn from the very basics, especially his control.
Selena often carried a massive amount of water by turning her ena into a bowl. By utilizing this concept, he could create a pseudo-telekinesis.
Then, all these parts were just the guns he tried to control purely with the new technique.
To shoot them, he planned to combine it with his Machine Gun Version. In Machine Gun Version, he created five bullets that would gather the ena from his body and form the bullet before shooting them in rapid succession.
