The College of Ikazaki City has always provided magi with a sanctuary; it's very existence was to teach such magi how to become skilled summoners. Such magi were trained to summon familiars within the College's very walls. These familiars fell under seven classes: Saber, Archer, Lancer, Rider, Caster, Assassin, and Berserker. The pairs became lifelong companions, for if one perished, so would the other.
The magi's futures were drastically changed when the Flower of Eden reappeared after one thousand years. The glowing ivory flower was said to grant a mage superior power above all else and grant their every wish, but at a cost-- their mind would be clouded with corruption, and eventually, they would become something entirely different.
A group of magi decided that they would take the risk, and set out in search of the mystical blossom. After a long amount of time searching for such a thing, the reached it before the College could, and kept it in their possession. As lore dictated, the magi were granted extreme amounts of power... enough to take over the whole of Japan. Within just one year, their reign covered the entirety of the nation, replacing the island's government with their own trusted.
While the rest of the nations struggle to deal with the traitorous magi's coup in the most discrete way possible, the other magi are ruthlessly persecuted by the new rulers' followers. They are driven underground in a last attempt to flee, but unfortunately for them, many beasts roam beneath the surface of the earth. The magi and their familiars must find a way to survive both above and underground as they figure out how to solve the chaos that has enveloped their very way of being.