Complex sentence: It tells the story of a Japanese boy of Korean origins (Kubozuka), and his love story with a Japanese girl (Shibasaki); however, the central theme of the movie is about the integration problems of a "zainichi" boy in Japanese society.
Split into simpler sentences: It tells the story of a Japanese boy of Korean origins (Kubozuka) and his love story with a Japanese girl (Shibasaki). The central theme of the movie is about the integration problems of a zainichi boy in Japanese society.