Do Min-joon is an alien who arrived on Earth in 1609 during the Joseon Dynasty and became stranded for over 400 years. He has enhanced abilities such as superior vision, hearing, speed, and teleportation. In the present day, he works as a college professor. Initially, he is cynical and detached, but his personality changes after meeting Cheon Song-yi, a top Hallyu star, becoming protective and caring. He falls in love with her, which significantly impacts his outlook on life. Throughout the series, he struggles with his immortality and the limited time he can spend with Cheon Song-yi, facing the dilemma of returning to his home planet to survive.