Shinko Aoki resides with her family in 1950s rural Mitajiri, Japan. Her grandfather, a former teacher, recounts the region's history as the ancient capital of Suō Province, igniting her fascination with the Heian period. This passion fuels vivid visualizations of Princess Nagiko Kiyohara's life a millennium earlier, an ability Shinko attributes to the distinctive cowlick on her forehead, which she dubs her "mai mai."

Energetic and imaginative, Shinko exhibits tomboyish enthusiasm for outdoor exploration and fearlessly embraces unconventional behavior. Her unrestrained curiosity drives unpredictable actions—wandering fields or launching spontaneous adventures—occasionally sparking minor conflicts with her mother. She forms a deep bond with Kiiko Shimazu, a reserved Tokyo transfer student grieving her mother’s death. Through their friendship, Shinko introduces Kiiko to imaginative play and local exploration, helping her adapt to rural life while weaving her into historical fantasies of Princess Nagiko.

Shinko co-founds the "Destiny Squad" with Kiiko and neighborhood boys, including Tatsuyoshi, the 14-year-old son of a local policeman. The group pursues ventures like damming a creek to rescue a goldfish, symbolizing shared hopes. Their innocent play shatters when Tatsuyoshi’s father dies by suicide after a gambling scandal. In response, Shinko joins Tatsuyoshi on a nighttime quest to confront those responsible, exposing her to adult hardships like crime and grief and forcing her to confront realities beyond childhood fantasy.

After her grandfather’s death, Shinko relocates with her family to the city, ending her rural childhood. Her departure leaves a legacy: the strengthened bond between Kiiko and Princess Nagiko in Shinko’s imagined historical tapestry.