From Friendship Scans:

Princess Thesia is a runaway alien who has just arrived on Earth while Annie, an extraordinary 17-year-old senior high-school student, is suddenly captured by Oscar, who takes her to another planet, Shuangxing Country. But because the way back to Earth has been damaged, Annie must wait three more years until she can return. Even after confirming that Annie is not Princess Thesia, many strange things happen around her, causing her to be once again mistaken as Thesia. All while Annie’s fantastic dreamland calls her to its unknown depths.