Master of the Forbidden Swords

In the world of Reidos, 70% of the planet was taken over by the Worldtakers. They released various kinds of monsters and seeked the annihilation of the human beings. However, they didn't expect that humans would also make use of the mana that they brought the their world. All humans had mutated and was able to activate the Reidos system, the last blessing of Reidos before resting. Half a millennia have passed and the humans took back half of the lands. In one of the human land recovery operations. A husband and wife adventurers found a child from a world taker's base. They didn't know who's child it is but they were certain that their wasn't a monster in his genes. Who was the child? What would he bring to this world? Only time will tell.