To Me, the One Who Loved You - Japanese Science Fiction Romance Anime Film

The film follows Koyomi Hidaka and Shiori Satō falling in love with each other, but their parents' remarriage has led them to elope to a parallel world where they are not stepsiblings. Its companion film, To Every You I've Loved Before, depicts an alternate version of Koyomi, named in that world as Koyomi Takasaki, meeting Kazune Takigawa, who introduces herself as his girlfriend in the 85th parallel world.