Because I'm Calling Your Name

In a world where people regularly travel between slightly different parallel universes, Koyomi Takasaki lives with his mother after his parents' recent divorce. Awkward and studious, he has trouble making friends at his new school, until his classmate Kazune Takigawa seeks him out. She claims that she's moved here from another world where she and Takasaki are lovers but could he be the one who's actually from a parallel world? Source: Seven Seas Entertainment

From Seven Seas: In Koyomi Hidaka's world, travel between slightly different alternate universes is commonplace. After his parents' recent divorce, Koyomi lives with his father and falls in love with a girl named Sato Shiori when they meet at his father's workplace. But their young love seems doomed when their parents get remarried—to each other. Is there some parallel world out there where Koyomi and Shiori can be together as lovers, not step-siblings...and what could be the price if they try to find out?