The world of Varries is at its peak. The slavery of The Faus and The Slaughtering of The Plas events are poisoning Varries' magic stream. Witches and wizards keep disappear suddenly because of it. To maintain their position in this world, they gather all of people with latent talents to use and control magic in a institute. Leodetable Institute is one of them, specially for wizards' apprentices.
The terms of "magic stream" here; you can say it's the varries' core. Just like FF7 Life streams. The looks is similar like lava/ earth's core. At other game of DV, it's called "The World's Lake". The cause of why this "magic stream" is poisoned will be explained in Leodetable Institute (LI). But how this "magic stream" works will be explained at other project. :3
The terms of "Fau" and "Pla"; In Varries, human is divided into three races, "Hum", "Fau" and "Pla". "Hum" is a normal human like us and have majority in number and culture. "Fau" is human half-animal. You can say werewolf, fairies, and medusa is included in this type. This race has a short lifetime with faster growth than hum. "Pla" is human half-plant. They lived longer than anyone and has slowest growth and reproduction. At the time they died, they will become voiceless plant. Their graveyard is the forest itself which become literally part of the magic stream.
The history of Varries' humanity is pretty damn long and explained in (almost) every projects DV has. Long story short, "Hum" and "Fau" agreed that "Pla" is dangerous for their life without knowing that the one who keep Varries stable is "Pla".
Everyone has the magic aura inside their body but different amount to each person. Magic Aura = Soul. These witches and wizards are the ones with "over-flowed" power. If they can't control it, they might destroy their own houses without their consent.
To know whom in this kind of situation, they use some methods like spreading the "invitation" letter which only goes to people who have over-flowing magic from them. In LI, there are certain levels of magic aura which they allow to be their magic (from level 6 to level 0).