In Another World My Sister Stole My Name (Manga) Vol 01 (Mature)

Through a handheld mirror connected to another world, college student Ichika befriends a boy named Cecil. But when the mirror disappears one day along with her older sister, Karen, Ichika thinks she'll never see the two of them again...until a year later, when the mirror suddenly turns up and sends Ichika to the world on the other side! There, she finds a grown-up Cecil and her sister, who for some reason, has become a saint named Ichika-!? After Karen has stolen her name and her life, Ichika must forge her own destiny in this otherworldly, doting fantasy!???? Yen Press
(W) Kotoko (A) Nikrome