Komamoto Kyota is a high school boy who dotes on his 3-year-old sister. His parents both work, so he handles all the housework and childcare at home. Akiyama Sumi is a beautiful, smart, but solitary girl whose intimidating presence keeps everyone at arm's length. When Kyota went to his sister's kindergarten entrance ceremony, he found Sumi there with flushed cheeks, snapping pictures like a pro photographer. "Gosh, how adorable...... she is!" They became friends and gradually grew closer as they learned that they are both taking care of younger siblings. They cook together, help each other pick up the kids from kindergarten, and go on holiday outings. Yes, their relationship is truly that of "mommy's friend." A romantic comedy about child-raising! (Source: Gagaga Bunko, translated)