Kōta Seto, a young boy in grade school, spends a lot of his time with his friend Mai Makihara due to her constant asthma attacks. One day while walking home from school, they find an abandoned kitten (which Mai names Blue) in a box in a park, and due to Mai's persistence, they end up moving it to a nearby shrine where they take care of it by visiting it daily and giving it food. Mai realizes that she is preventing Kōta from playing with his other friends, and one day Kōta agrees to play in a soccer game while Mai goes to check on Blue. That day, it starts to rain, and on her way home, Mai is taken to the hospital and soon after dies. Kōta blames the cat for Mai's death and intended to leave it for dead, but Momo, a shinigami, intervenes and gives Kōta the chance to speak with Mai once more, who asks for Kōta to care for the cat as her final wish.