Natsumi Mizuki, a fourth-grader in 1992, unexpectedly becomes the caregiver to her time-displaced infant daughter Mirai, sent back from 2007. Temporarily placed under her aunt Izumi Shimamura’s supervision due to her parents’ delayed travel plans, she navigates school obligations, secretive childcare, and maintaining friendships while preventing temporal disruptions. Her bond with escape-artist dog Bobby persists through multiple separations, his loyalty mirroring her own dedication to protecting Mirai. Proficient in Japanese and physical education, she hones cooking skills and masters unicycle riding, though academic performance wavers under childcare pressures. She resourcefully employs a futuristic communication device for parenting guidance while concealing Mirai’s origins.

Her dynamic with classmate Daisuke Yamaguchi deepens through collaborative caregiving, his steadfast assistance gradually fostering mutual romantic feelings that later lead to marriage. Initially contentious interactions with Izumi transform into cooperative partnership as both adapt to Mirai’s needs, aided by grandmother Kinuyo Mizuki’s childcare wisdom. Personal quirks include a stuffed animal collection, needle phobia, and seafood aversion, juxtaposed against her eventual career path as a flight attendant. The narrative traces her maturation from reluctant guardian to confident multi-tasker, balancing youthful interests with accelerated responsibility, all while preserving Mirai’s place in her reconfigured daily life.