A stray dog wanders into a high school's grounds. The dog, named Kuro, stays at the school and becomes a special friend to everyone. Ryosuke and Koji are not only best friends but also rivals in their love for Yukiko. One day, soon before the upcoming university entrance exam, Koji passes away in a bike accident. Yukiko, who did not reciprocate his love, feels devastated, but Kuro helps heal her pain.
Twelve years later, Ryosuke is now a vet and goes back to his hometown and meets Yukiko again. Ryosuke confesses his lasting feelings to her. Kuro has remained her pet, but is now very old and dies of an illness. Yukiko, who has had never gotten over the pain of Koji's death, faces Kuro's death and accepts it. This allows her to open herself to Ryosuke's feelings. Taking his hand, they begin a new life together.