I really didn’t find much in the way of music stuff in Japan while I was there, but I can recommend some stuff that has stuck with me in the years since.
the scale of Tokyo is overwhelming, but I’d recommend seeking parks and some smaller neighborhoods if the big stuff winds up feeling too big. I loved shimokitazawa and yoyogi park. even the big stuff is clean and orderly in a way that will feel foreign and futuristic, but I loved the small stuff the most.
Osaka was my favorite city. if you eat meat, I had some really great moments with the chef at Nikuteria Carnebaka. go out one night at eat fried stuff and drink. go up Mount Koya and walk through Okunoin (can’t really stress this enough, it was probably my favorite part of a month-long trip).
also, if possible, get outside the cities. half of my time there was spent in onsens in small mountain towns and that, more than the city stuff, is what has me itching to return to the country.