Kawada Michiyo (Kimura Yoshino) lives happily with her husband Daisuke (Kitamura Kazuki) and their three sons. But one day, their lively 4-year-old second son Yuhei (Yokoyama Ayumu) who loves sports, catches a cold and is brought to the hospital when his fever does not subside. Yuhei is diagnosed with a cancer called hepatoblastoma which occurs in 1 out of 1 million people. Michiyo decides to call it a "worm" after discussing with Daisuke and encourages their son to be hospitalised so that he can beat the "worms" in his stomach. Yuhei bravely tolerates chemotherapy treatment, which is tough even for adults, and only has smiles for the family. However, Michiyo is told that Yuhei has no chance of surviving two years. She refuses to give up no matter what happens.