I dare say that considering Japan is (one) of the foremost superpowers in the world; Japanese cultural influence would appear in many places -- while the 19th century is largely European inspired, seeing the expansion of opera, traditional music, etc. in Japan -- Japanese people will eventually bandwagon and seek to meld Japanese culture with pop and rock music. Japan's roots in creating punk, rock and pop music comes largely from the Indonesian War (like Vietnam with America OTL), and influences the anti-establishment discourse that leads to the Syndicalist Revolution of 1979, spear-headed by the Syndicalist-Socialist alliance, leading to the United Front with Bernard Sanders at the helm. So, counter-cultural music still very much exists, and I expect the Confederates/Canadiens to put out a large amount of it -- stuff like Creedence Clearwater Revival, and such.
But as a result of Japan's early cultural "brain-meld" with Britain and the prolonged Anglophiliac sentiment, you'd see Japanese music ranging from stuff similar to
Queen, all the way to the traditional J-Pop music commonly acclaimed by weebs.
As a result, you'd see Japan exporting a lot of it's music overseas in much the same way as America -- pop music, punk music and some rock-esque stuff.
I mean, Meiji as a spiritual icon has spread far beyond Japan's borders, making appearances in many faiths.
Britain and Japanese influence would probably be seen in albums like
Yoshimi Battles the Pink Robots, which would be an album produced in the Confederate States. OTL, the album was very poppy mixed with traditional rock, influenced heavily by Cat Stevens/Yusuf Islam. IATL, it would be influenced largely by J-Pop's synthy stuff, British music, and "generic" rock. That very same album was given high praise by the Japanese media.
However, chances are that music such as
B.Y.O.B.,
Mosh, and other 21st century anti-war music would likely not exist. If it did, it would form itself in the form of sentiment against oppression (see: Germany fucking around with Denmark, for example?)
But I mean, these factors combined should allow for a lot of familiar culture to exist (
Another Brick in the Wall,
Welcome to the Machine), and most music that directly addresses Vietnam would be substituted for Indonesia, like Full Metal Jacket. Confederate States Marines Corps soldiers training at Parris Island before being shipped out to the Japanese front-line in Java, with Pvt. Joker photographing Japanese and Indonesian atrocities; meeting the Empress (she did serve as a front-line soldier in the 1960s, choosing to go off to fight, confident that she would see to the end...)