When sana and tzuyu were little girls they were seperated but they promised each other that they would be together forever.But when tzuyu comes back to reunite with sana,she and tzuyu find out that they will be together in a girl group called twice.But tzuyu and Momo(Tzuyu's college girlfriend)are married and are both also gonna be in the girl group and still have permission of the company to be a married couple and be in the girl group at the same time