Komamoto Kyota, a high school student devoted to caring for his 3-year-old sister due to his parents' busy schedules, forms an unlikely bond with Akiyama Sumi, a stunning yet aloof classmate. Their friendship blossoms during a chance encounter at his sister's kindergarten event, where they bond over shared responsibilities of sibling care. Through shared moments of cooking, childcare, and outings, they develop a unique 'mommy's friend' dynamic, blending comedy and romance in the realm of childcare.