Invincible Tower Defense in Another World

This is a world where force is supreme. The breath of the deep sea monster forms an endless storm... The steps of the lava giant destroyed cities one after another... The demon of the abyss wants to invade this world... Human beings rise up to practice, the mages call for wind and rain, and suppress aliens; the knights cut mountains and rivers, and travel the world! The sky, the earth, the ocean, mages, knights, aliens... The four great empires of mankind only occupy a corner of the endless continent.