OH LUCY! follows Setsuko, (Shinobu Terajima), a single, emotionally unfulfilled woman, seemingly stuck with a drab, meaningless life in Tokyo. At least until she is convinced by her niece, Mika (Shioli Kutsuna, Deadpool 2), to enroll in an unorthodox English class that requires her to wear a blonde wig and take on an American alter ego named Lucy. The new identity awakens something dormant in Setsuko, and she quickly develops romantic feelings for her American instructor, John (Josh Hartnett, Penny Dreadful, Pearl Harbor). When John suddenly disappears from class, Setsuko travels halfway around the world in search of him, and in the outskirts of Southern California, family ties and past lives are tested as she struggles to preserve the dream and promise of 'Lucy.'