Two girls are friends, "sisters," and soulmates. Yu Qi, a 17-year-old high school student, wakes up to find that she and her 27-year-old self had switched souls. One has to relive the experience of meeting her lover again and the other has to bear the responsibility of being a girlfriend, despite being unfamiliar with the girl she's dating. Both worlds are always changing, but the only one who never changes is… you, who is always by my side.