In Another World, My Sister Stole My Name summary:
Ichika, a college student, was interacting with a boy named Cecil from another world through a hand mirror she held in her storeroom. One day, her older sister, Karen, suddenly disappeared, and at the same time her hand mirror also disappeared. A year later, as soon as Ichika picked up her hand mirror that she found by chance, she was sent to another world. There was Cecil, who had grown older, and Karen, who had become a saint by calling herself Ichika for some reason?! In a world where her name and memories are stolen by her older sister, a different world doting fantasy opening up for her destiny!