The main effect of Western influence on Japanese culture was to make Japan's culture more like the West and to contribute to the decline of traditional Japanese ways.
Let us look at a couple of ways in which this has happened. First, we can look at food. Japanese eating habits have changed very much through Western influence. Japanese eat things like ham and eggs and hamburgers and Bavarian cream puffs now as a normal part of their diet. Second, we can look at sports. While sumo is in some ways still the national sport, it has lost a great deal of ground to baseball and now even to soccer. These Western sports have become extremely popular in Japan.
In these ways and many others (men almost never wear kimonos any more, for example) Western influence has affected Japanese culture.