Chiyomi, is a high school girl who was born and raised in a retro Showa-era shopping district in Shonan. She is a member of the basketball club and has a kind personality that stays cheerful despite her somewhat complicated family structure. She and Minami-kun, also known as Minami Hiroyuki, a basketball star from her hometown of Shonan, have been like siblings since childhood, and they are happily in a relationship. However, one day, he suddenly becomes 15cm in size and fits in the palm of her hand. Chiyomi begins living with him in his now tiny body. Adapted from the manga series "Minami-kun no Koibito" (南くんの恋人) by Uchida Shungicu (内田春菊).