The Great Mage from 5000 Years ago

Humanity was in a state of peace and people in this Days are living normal like working, and Having a family, But They never expect the day when They realized that they are not the one at the top of food chain rather they are at the bottom, People have discovered Monsters, Ancient beast, And Demons that lurks through the woods, people on that Era always got Killed or become a slave of the demons, humanity don't know what to do, People in earth are getting lesser and lesser every year that passed, but all of that change when A group of Friends have discovered a way to defeat this Monsters and make human rule the Earth again, and The leader of this Group was Karl Quail The First Mage and The Greatest of all Mages, they have defeated almost all the Demons and beast They have encountered Resulting humanity to once again rule the Earth, for the Earth to not be over ruled again, The Group of friends have teach the people how to defend themselves, They have teach them in a 4 Skill category and this are Being a Fighter, A witch, An inventor and lastly a Mage, This skills Can get stronger by the grade Level that has been reach of the person who was learning or Training it, the Grade level is from 1-20 Levels, and of course the lowest was The Grade level 1 who has the strength of an ordinary human, people has became strong and the Group of friends became a legend, But unfortunately Karl Quail suddenly disappeared resulting the group to fall apart, Making humanity once again in a reach of Vulnerability, But The Humans didn't give up and continue the legacy that the group of friends have made, through the years they have evolving their life style that it came to the point that people have became rude to people with lower grades, And the people with Higher grades and Rich Families has been treated like royal, But what Will happen if The Great Mage have reincarnated in a body of a lower grade? and it's been 5000 years and Everything change for are Great Mage,