On September 9th, the day of the Katakai Fireworks Festival, high school student Hana (Tanimura Mitsuki) comes home from the hospital after six months of treatment for leukemia. She then discovers that her older brother Taro (Kora Kengo) has become a hikikomori (social recluse). Taro used to be tender, smart and proud of his younger sister, but now he even turns his back on her and stays in his room. Her parents act like there is nothing wrong with him.
Later that evening, Hana attends the Katakai Fireworks Festival and observes the town's youth group happily planning for next year's event. She decides to get Taro involved with the group in an effort to bring him out of his shell. Hana drags Taro out of his room and to the youth group office. Unfortunately, Taro is not accepted as a member. Hana, nevertheless, is determined to get Taro back into society and helps him find a part-time job as a paper boy & into the adult meetings for the Katakai Fireworks Festival.
With Hana's help Taro slowly opens up to the world again. Then, with winter approaching, Hana has a relapse with her leukemia. Taro comes to the hospital everyday to visit Hana and soon learns that the Katakai Fireworks Festival is a symbol of happiness for Hana. Taro then takes the initiative to make Hana happy and approaches the town's youth group once more for admittance.