It is beautiful to see the actual scenery and villages of that time, almost as in a documentary, although I must say people were very poor as well - Japan was in a deep recession. The film was based on a story by famous author Kawabata Yasunari and contains references to his story "The Dancer of Izu," that is set along the same road.
There is not much of a plot, except one red thread, a mother (Futaba Kaoru) who is so hard-up that she has to sell her seventeen year old daughter (Tsukiji Mayumi) into prostitution. This is not told us up front, but becomes gradually clear. She is taking her by bus to the station where the daughter will take the train to Tokyo, a city "full of badgers and foxes." Many daughters from the poor peninsula have made this journey and none has ever returned home, we learn from the conversation of other passengers. But we also see some tender feelings being born between the still unmarried driver and the girl, so perhaps there is hope...
Other passengers include a modern woman (Kuwano Michiko), who smokes cigarettes and drinks liquor, so she probably works as a hostess in a bar in Tokyo. She openly flirts with the driver and puts down everyone she dislikes, such as a self-important loan salesman with a huge mustache (the man is very proud of this appendage and there is a comic scene when another passenger boards with exactly the same mustache).
But the heart of the film is the driver, who chats friendly with the locals, delivers messages for them and is helpful to everyone. He is a sign of steadiness in the turbulent economic times. He had saved money to buy a second-hand bus himself, but now he uses it to help the mother and keep the seventeen year old girl out of prostitution (at the suggestion of the outspoken woman). This is not shown or explicitly mentioned, but in the final shots we see how the next day the girl and her mother return home by the same bus. Presumably, the bus driver will marry the young woman.
Arigato-san was made by Shimizu Hiroshi (1903-66), a friend and colleague of Ozu Yasujiro at the Shochiku studios. This light but uplifting film has become available thanks to the Criterion Collection.