[ possible romance later on ] Exo is a planet which is support by the Tree of Life. The Tree of Life is protected by twelve guardians. There are twelve guardians for every other generation. Each guardian has a power of their own which they must discover for themselves. The guardians are to stay with the Tree of Life until their death which may take hundreds of years. The new guardians will take place of the older ones as they go to live in peace with the Tree. The guardians protect the Tree from the Darkness that had once consumed Exo. The Darkness is becoming stronger once again, the Tree grows old and fragile. Only the guardians will be able to save the world of Exo.