Living by himself in the city, Tarou Tsubaki runs into his once-divorced childhood friend, Hiraiwa, who lives with his daughter, Fumio. Their unexpected encounter puts into motion many changes in Tsubaki's life. Tsubaki-kun fits in perfectly with Hiraiwa and his daughter, and over time, colorful bonds begin to form between Hiraiwa's family and Tsubaki. Tsubaki's Diary is a tender account of the vibrant and empathetic connections that form in everyday life.