Natsumi Mizuki is a fourth‑grade student whose parents have gone to London, leaving her under the care of her Aunt Izumi. Izumi, an aspiring manga writer trying to land her first big break, has little time to attend to a mysterious baby that appears out of nowhere on Natsumi’s very first night alone. The infant, named Mirai, is actually Natsumi’s daughter but 15 years older, and she somehow traveled back in time. Now, the young girl must raise Mirai while maintaining her school life and keeping the existence of the baby a secret from everyone. With the reluctant help of Aunt Izumi and a collection of futuristic baby‑care gadgets, Natsumi navigates the challenges of motherhood and adolescence.