Silver ring and the wars

There said by the legends that there existed that there existed thing called the 'silver ring' that grants wishes of the winners of the war that itself created. Though, the legend is only known to people who wants the grand prize, to some people, it is nothing but a legend. Every ten years, the ring becomes active and chooses 12 people to start the war for itself. It chooses people who are special for themselves and uses magic (mage). In the right time, they summon servants to fight with them. Only 1, along with the servant will be able to commit it. After that, the master needs to protect the ring until it is activated and if they lose it, they will be cursed for eternity. There was a legend behind it that started everything that has begun. One participant is Takumi Yamada with his lover, Airaka von Schzintch. He summoned a servant and he was disappointed with the results, resulting for him to make his lover her master to avoid consequences.