Kaoroke is probably one of the most popular pastimes in Japan and in many other parts of Asia. However, it comes with its own set of rules in Japan. People are expected not to join in when someone is singing karaoke and to let that person finish their song. Interrupting or joining in can be interpreted as being rude or offensive, so it's best to wait your turn when you're out singing karaoke.
Karaoke is on of the most popular activities in Japan, so visitors can bet that they'll find themselves out doing karaoke at one point or another while in Japan.