The term "Elf" in "Elf Swordsman" does not refer to the elves of an alien species, but to the pervasive spirits of elements.
The world has essence, and all things have spirit; vegetation, soil, stones, even abstract concepts and knowledge can be nurtured and grow in the tide of magic element, then descend to the world as magic creatures.
But this process is not instantaneous; before gathering enough magic power to be born as a sentient being, the ambiguous stage between elements and magic creatures is called "spirit."
Although summoning techniques only apply to high-tier Demon Kings or fantasy species, and were popular in ancient times when magic creatures were served as gods, strictly speaking, it is a spell already obsolete by the era.
But at the Royal Capital Academy, there's a magic subject called "Summoning."
