Ai-oon is the disappointing twin of successful and beloved Ob-oom. They aren't close. On Ob-oom's wedding night, she takes Ai-oon aside and makes a request of her. Ob-oon and her husband Paul will be going away for their honeymoon and she'll be leaving something important behind: a lover, May, she hasn't broken up with—and she wants Ai-oon to do it for her. In the early morning following the wedding, Ai-oon learns that the newlyweds got into an accident. Paul has passed away and Ob-oom is in a coma. When Ai-oon decides to fullfil her sister's request, she's shocked to learn that May is both blind and a woman. She finds herself unprepared to complete the task.

Bonded in their youth and separated by tragedy, an astronaut and a free diver bend the laws of space and time in their efforts to be together again.