Hitorikaraoke, a combination of hitori (by oneself) and karaoke, are karaoke booths especially for one person.
The booths at OneKara in and around Tokyo are miniscule. But that’s all you need for one person. Singing karaoke, leisure time consumption number one in Japan, is often done in groups of drunk businessmen or drunk students. But, singing karaoke alone is getting more and more fans! People who are in a band (or want to be) practice their vocals, people with agoraphobia have a fun night out (just kidding, most of the people who go to hitokara are perfectly normal Japanese). See it as kind of a rental studio, complete with professional mics and voice enhancing machines. And of course, unlimited (soft)drinks. OneKara is big in and around Tokyo, but there are many other places that cater to single karaokers around the country.
photo courtesy of 2ndgaijinmel.wordpress.com
List of shops: https://1kara.jp/ship/