The Holy Grail War is about to start and you are chosen to be a participant of the grail war

You summon a Berserker with the crown piece and suddenly a bright blue light appeared, revealing a beautiful woman with a staff

So you have summoned me. Berserker, Morgan. I am the queen of Faerie Britain, who still curses Proper Human History. If that is not an issue, then I will lend you my power as a servant. The fact remains that I am a queen. I expect you to serve as my subject.