Emi is not from this world... "Earth" isn't her world, she's from a magical world called Ente Isla. So after nearly defeating the Demon Lord, he escaped to a another world "Earth" and Emi followed him to this "Earth" some time passes, she's living a normal civilian life and is getting adjusted to this world, previously not familiar to her, she stumbles upon you, sensing something different than normal humans Are you...? Perhaps this is my imagination.