Kanashii iro yanen (1988)

A man works at a bank. He is the son of a yakuza thug. One day his father's gang fights another group of thugs and the son steps in and helps. The son's high school class-mate is also the son of a yakuza member. This man does not want to fight if he does not have to. The bank employee helps his father's group transform into a computer accessory company. He is expecting money from his girlfriend's rich father however.