It’s the 21st century, the Sword Master, the Demon Lord, and the Aliens RAW novel

Suddenly, a mysterious alien arrives.
The Nova Space Federation orders Earthlings to leave Earth.
Chen Il, a former sword master who was quite successful in his previous life, took up the noble sword again for the sake of humanity, but he can’t escape his status as a student and has to go to school.
In addition, the Demon King, who has been trying to take control of the Earth since the beginning of time, is the first to declare war on the aliens.