Castellian is a magical place where Caster resides. Casters are the ones who are tasked to close dungeon gates which is a portal for monsters to cross from the underworld towards Castellian. They took an important task to keep the place safe. Together with the Guardians. Guardians are special beings that could lend their power and assist Caster in closing the dungeon gates. The Casters and Guardians had a peaceful history but was changed when Casters got a little greedy. They asks Guardians for help but would take them as a bait or as a sacrificial lambs. Ellie, who is a Guardian witness this betrayal and decides not to help any of the Casters anymore. But her Mother pushes her to observe a boy and let her decide if she ever help him or not. And since she was a little curious of the weak boy that is a direct descendant of Night, she went onto Castellian to observe. But with a broken teleportation clock, instead of teleporting onto the present time. She was teleported years ahead of her time, that glitch completely altered the course of the relationship between Casters and Guardians.