Duel, Hit with All Your Strength!

Humanity ushered in peace, but crises continued. One day, an unknown person ushered in, which humans called an "alien beast." In order to fight against it, humans organized a "scientific defense force" to fight, and the losses on both sides were extremely serious. In order to eradicate this phenomenon, mankind has spent 20 years and finally figured out the reason for their emergence. Now we are about to usher in the final decisive battle...