To become a guardian on planet Lune, you have to win the guardian exams by completing the different missions and obtaining the respective stamps. To do so, a partecipant have to be in a group of three: the candidate, an helper-sponsor and a magicless creature that has to be protected during missions; and that creature must be a human from planet Earth. The human is allowed to help the aspirant guardian and he's in charge to hold the stamps collected.There are many other rules written on the guide that's given to the helper-sponsor at the beggining, they must be followed or you could get expelled.
The missions take place in different areas of planet Lune, and to be teleported there, the partecipant must know how to decode a "code spell" to create a "Lune Fragment" which is one of the few forms of teleportation.

The partecipant Yokun chooses his childhood friend Rei as the helper sponsor. And for the human, he chooses a teenager from a little town in the mountains, Haru.