Invisible Enemy

The more that enemies are knocked over, the more they became invisible.
They are called the invisible enemy.

Against this invisible enemy that had destroyed neighboring countries,
the greatest sword wielder in the country was tasked with thinning them out.
The sword wielder’s name was Anna.
She is the daughter of the legendary swordsman Oliver.

Oliver frowned on his daughter being placed with this thinning task, but,
Anna resolved to fight to protect the country, and started out on her journey…