A hero's destiny (Unknown destiny)

From the very old times, humans used swords or spells to defend themselves, but the demons who were stronger with their physical abilities and magic destroyed anything in their way.

Behind them was their king, standing with a satisfied look in his eyes at the sight of this calamity, and around his neck was something bright, which seemed to give him an incredible amount of power, it was my necklace.

"Do you mean that I should keep that dangerous thing knowing it doesn't even belong to me? Sorry grandma but I think I already gave it to him in his human form in my school's sellar."

"I knew this was going to happen, still I didn't expect for it to take place quickly. It looks like my plan to put all my magic as a barrier to protect you was useful, but as I become old, I could use it just once- ."