The World our Protagonist used to be is a modern era of technology where knowledge of humans reign over the world..
But The world he regressed is little different.
About 700 years ago due to long wait of demons they were able to come out of the the hell and started destruction.
Watching this the god to prevent humanity from extinction and create balance, he started to give blessings to the choosen ones known as mantra users/mana users.
These Mantra users were able to use mantra/spells to defeat demons and the spells are ranked
From highest order to lowest as follows:: creator level >Universal level>Planetary level>God level>MasterLevel>Advanced level>Intermediate Level>lowLevel.
But there is special type of spell which still unknown to mankind which can be both constructive and Destructive.