The first time I went to karaoke was 2016 in Osaka, as we went with a group from a hostel to a nearby karaoke bar. Was like a normal bar, but there were also two screens to showing the lyrics of songs, two mikes and a tablet to select the songs you wanna sing.
As we were a group of mostly foreigners, we chose many English songs. But at same point I wanted to have a go on Japanese songs. The thing was just at that time I even though I was able to read hiragana and katakana - my reading speed wasn't really good enough to keep up with speed as the lyrics are running through on the screen. So I needed a song which I need knew at least a little bit. So I tried the first DBZ theme song "Chala Head Chala" from Hironobu Kageyama. I struggled, but I was happy that I tried.
Two years later after moving to Tokyo, I started going to karaoke boxes with friends more regularly and with my constantly improving Japanese skills I got more confident trying more and more songs. I even started practicing at home by using lyrics videos available on YouTube.
Now I can feel confidently sing "Chala Head Chala", "Dan Dan", "We gotta Power", "Kimi ga ireba" and many more. I keep trying many new songs from Dragon Ball, One Piece, Detective Conan or even Slam Dunk .. It's endless. "
I even tried crazy stuff like "Ultimate Battle" (究極の聖戦) from Akira Kushida. Those who have seen the Tournament of Power in Dragon Ball Super know what I'm talking about^^
Last November I went with a Japanese friend to karaoke for three hours to only sing Dragon Ball and/or Kageyama-related songs. We found several songs from videogames or old movie endings which I knew from hearing, but never tried singing. I gave it a go and wasn't too bad.
So therefore I can safely say that karaoke is a good way to get confidence in your Japanese. The more you try, the better you get and it improves your reading speed. Especially when you try songs from which you know the melody, but not the lyrics by hearts.
If you are learning Japanese and live in Japan, definitely give it a go! And if you a lacking confidence, get a drink before you start^^