May be one of the big difference among interiors of Japanese trains and European trains are that Japanese trains have a lot of ads, advertizements hanging inside the trains. Advertizements in European trains are usually on the walls and Japanese trains have these advertizements too.
Usually the ads on the walls are for long period advertizing but the ads handing from the ceilings are much shorter periods, therefore these ads are for announcements for campaigns. These campaigns are usually of department stores, shopping malls or retail stores.
Also there are a lot of ads for magazines and books too. Due to there are so many magazines published each week as weekly magazines, ads in the trains are the major way to let the people know about the magazine and also what is written inside the magazines.
Therefore usually sensational titles and texts; scandals of Japanese celebrities and politicians, appear on these ads which make the passengers to motivate buying the magazines.
These ads are major income for Japanese railway companies and there are more ads in the metropolitan area and of course in crowded trains than in the rural area and trains running there.