Sayonara, Kuro (2003)

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.