Kanata (NOGISHI Konoha) and her younger sister Sumire (IKEDA Nonoka) have been living apart since their parents' divorce. Kanata is having trouble adjusting to her new school and is spending her summer holiday helping her mother run her snack bar. When Kanata's mother suggests that she go to her grandmother's house for a final summer holiday memory, Kanata heads into the countryside. Once there, Kanata can't hide her annoyance at the innocent Sumire who bubbles with enthusiasm for the time they will spend together but a trip with Sumire in search of fireflies, which are not supposed to appear during the summer, forces the lonely teen out of her shell.