Isekai de Ane ni Namae wo Ubawaremashita  

In Another World, My Sister Stole My Name, 異世界で姉に名前を奪われました

Using a device that connects to another realm, a university student named Ichika forms a bond with a young man named Cecil. However, when the device vanishes along with her older sister, Karen, Ichika believes she will never see them again...until one year later when the device miraculously reappears and transports her to the other side! There, she discovers that Karen has become a saint named Ichika, but for some reason has taken her identity and life. As a result, Ichika must create her own path in this fantastical, loving environment.