Well I'm sure you're aware that since WWII America has occupied Japan (their are US Navy bases in Japan to this day).
Gee, who on the planet isn't aware of this?
Inevitably the Japanese have been exposed to massive doses of American culture, and that influence is very evident in their own pop-culture. For example "Hideki" or "J-Pop" is unequivocally western style music
Yes and European and other Asian countries as well... Japan has always been a nexus point for culturedumping (and invariably blending their own uniques aspects to it to create something new)...
"J-Pop" isn't really "western" music either, although it does borrow from it. Kayokyoku (Japanese pop music), came about from blending traditional songs with pentatonic rhythm. Enka (Japanese folk) singers popularized it...
The 50's in Japan were all about latin music and the 60's were all about British rock bands...
The J-pop you hear today is born out of kayokyoku songs "cheapend" in the karaoke boom into disposable pop (now often taking advantage of several of the onomatopoetic aspects of the Japanese language itself)...
Of course this just focusses on "pop" music and doesn't get into rock, folk, classical (both Japanese and European), R&B, or Hip-hop and Rap...
However if you *ARE* looking for strictly Amercian influence than look no further than the quintessential American music; Jazz... Ironically Japan is bigger consumer of the genre than the country it was born from...
(even to the point of mixing in english lyrics)
This has more to do with sprinkling English in daily language is "catchy" (much like you see English often littered with French, although I wouldn't go so far to say that American culture is french culture through an American filter)... Besides 6 years of English is compulsory for all Japanese students anyways (although they're still not very good at it and have come to distinguish English and "Conversational" English as two different things), is it's inevitable that the language is going to have words that creep into daily use (although there's plenty of French and German that work their ways into it as well)...
and like I said most Anime charachters look western.
Actually most anime characters look their part... I don't think "western" is the right term since they don't really look that either... I'm not sure if it's the big eyes (simple technique to expose more emotion) or the hair styles/colors the seem to make many people think think of them as "western"... (I think it's just self projection personally)
But the American influence in Japanese pop-culture is a simple sociological fact.
There's no doubt about that, and you can say that the opposite is true as well... But you didn't say it was influenced, you said it *was* American culture through a filter (which is quite different)...