I'm just issei

During the great war the event in which God was sealing the beast 666 in forbidden seals the beast made a huge sacrifice splitting it's body into 7 cores orbs 6 of the orbs escaped and we're found by God and since he was to tired he didn't have the right amount of power to do everything and decided contain it into a box and bury it along with the holy Grail and the pugatory dragon kurenai the order dragon scared gear to gaurd the box

Find out what happens when a young boy by the name issei hyodou find a box buried on his backyard