Koume Asakura is a first-year middle school student who lives alone in a house most of the time. Her mother died when she was very young, and her father is constantly away on business trips. Her only real support is her next-door neighbor and childhood friend, Mao Hagino, who checks in on her and often eats meals with her. Koume has a secret crush on Mao but cannot bring herself to confess. One day, rummaging through a box of souvenirs her father brought back from a trip, she finds a piece of paper with a spell that supposedly lets her see the future ten years from now. Curious about who will be by her side in the future, Koume tries the spell in front of a mirror. Instead of seeing her future self, she sees a baby girl reflected in the glass, and moments later the baby climbs out of the mirror into the present. The baby, named Ai, is Koume’s own future daughter. With Mao’s help, Koume decides to raise Ai until the baby can return to her own time, and the two middle schoolers take on the roles of makeshift parents.

The story follows Koume and Mao as they juggle school, friends, and the everyday challenges of caring for a rapidly growing infant. Ai, though a baby, is unusually curious and active, leading to constant mishaps and heartwarming moments. As they work together, Koume’s feelings for Mao deepen, and Mao becomes increasingly devoted to Koume and Ai. Their relationship evolves from a childhood friendship into a romantic partnership, all while keeping the secret of Ai’s origin from the outside world. Koume also grows stronger emotionally, finding a sense of family and purpose she never had before.

Major narrative arcs include the pair’s efforts to keep Ai hidden, Ai’s gradual development from a crawling infant to a toddler who can walk and speak simple words, and the emotional crisis when Mao is faced with his family’s potential relocation. The most poignant arc occurs when a magical mishap transports Koume, Mao, and Ai back in time, allowing Koume to meet her deceased mother and receive the closure she has long needed. As Ai’s stay in the past nears its end, Koume and Mao must prepare for the inevitable farewell, knowing that Ai will return to the future where she belongs.

The original series concluded with Ai’s departure, but a sequel, Hello! My Baby S, picks up three years later. Koume and Mao are in high school and still together, eagerly awaiting a chance to see Ai again. When Ai reappears through the mirror, she brings her little brother from the future, expanding their surrogate family once more. The core characters remain Koume, a determined and kind-hearted girl; Mao, reliable and quietly affectionate; Ai, a bright and mischievous force who brings everyone together; and supporting figures such as Koume’s father and school friends. The setting is a typical Japanese town, anchored by the two neighboring houses where much of the heartwarming child-rearing comedy unfolds.