When a girl and her older cousin who thought was gonna be a boring summer takes a turn when they now protect not just theirs but also different universes but with other people from other universes that they meet along the way

Years later after the battle against the Severant, Sarah now an adult created a school to make new protectors. For it was Elysia's wish... before she went missing during a solo mission

You all know how Sarah and Lucifer first met but in this story you'll get a proper backstory