Natsumi Mizuki is a 4th grader whose parents have gone to London. Her Aunt Izumi comes to live with her. Izumi is an aspiring manga writer who is trying to get her first big break, so she doesn't have time for a baby that appears out of thin air on Natsumi's first night alone. The baby's name is Mirai and her mother is *Natsumi*, but 15 years older. Somehow, Mirai had traveled back in time. Now the young Natsumi has...